Enable privacy dropdown even when saving an annotation is disabled

 * Remove the 'line-height' property from .dropdown-menu-btn that,
   combined with default top/bottom padding for <button> elements
   was causing the button label to be vertically off-center in
   the 'Post to' button.

 * Remove duplication between .primary-action-btn and .dropdown-menu-btn

 * Use $color- variables for palette consistency in .dropdown-menu-btn

T-125

 * Implement design change to allow a user to change the privacy
   setting for an annotation even if the annotation cannot
   yet be published because no tags or text have been entered.

 * Disable the hover state for the main section of the button
   when it is disabled.

T-125

Server-rendered login form

Replace %20 with space when displaying filenames etc

Remove special-handling of pre-groups annotations

T88 - Add ability to leave groups

Add a new cancel/leave icon next to private groups
in the groups list and invoke groups.leave() when clicked.

Leaving a group invokes the as-yet-unimplemented
'POST /groups/<id>/leave' endpoint on the server.

T-88

Inline the H icon font

Fix race for session data on startup

The previous fix to use an absolute URL to the icon
font did not work in the Chrome extension because
the base path for assets was different.

The proper solution here will involve refactoring
the CSS build pipeline and possibly automatically
inlining font URLs in the process. I did not just
add a preprocessor to inline all URLs because
that would also have affected fonts in katex.min.css
and added significantly to the size of the CSS bundle.

This commit reverts back to the previous solution of
inlining just the icon font.

See #2571

Several parts of the application require access to the session data
fetched from the server when rendering. On first page load we don't have
this data (something we can fix in the future by inlining the data with
the viewer HTML) and this resulted in a race between the session data
load triggered by `checkAuthentication` (in config/identity.js) and the
query sent to the server by `WidgetController`, which needs to know the
current focused group id.

Fix this by ensuring that the first load of session data is complete
before switching views -- achieved by adding an item to the list of
dependencies passed to `$routeProvider`.

This works, but results in multiple requests for session data in quick
succession, because `checkAuthentication` runs while the view is
loading. To resolve this problem, we add a straightforward TTL check to
the `session.load()` method, and only make a new request if the data is
more than 5m old.

Session data will be overwritten as normal whenever session mutating
methods (`session.login()`, `session.logout()`) etc. are called.

Fixes #2590.

Pulling the server-side template and rendering it with swig is bound to
break if we change the way the form is rendered on the server-side (as I
am in the process of doing).

So, convert this from a sort-of-integrated test to a unit test.

Extract the WebSocket client into its own module and add tests

In preparation for adding additional push notification types,
separate out the client into its own module and add tests.

T-105

Do not show vendored PDF.js in language stats

Group landing pages redesign

 * Implement new look for the Create, Join and Share groups pages.
   The forms are functional without JS but contain a small amount
   of JS logic for enhancements such as selecting the content of
   the share pane.

 * Merge the 'Login to join' and 'Join' pages into a single
   form. The only difference between the two is that
   when the user is not signed in, the button label
   changes from 'Join <Group Name>' to 'Sign in to join <Group Name>'
   which redirects to the login page.

 * Create a new site.scss file which is intended to
   contain only styling for the website and a site-bundle.js
   bundle which contains JS code used only for the site.

 * Extract out the button styles used by <dropdown-menu-btn> into
   a separate .scss file for re-use

 * Add additional colors used by the new group forms
   to variables.scss. To avoid the problems
   with naming that arise when trying to insert additional
   colors into a list with names like 'light', 'lighter' etc.
   I'm starting to use http://chir.ag/projects/name-that-color for
   memorable names.

 * Start to use a '$color-' prefix for colors, in preparation
   for extracting colors into their own file.

Card 93

Re-implement filtering of annotations based on the current selection

44edb50b18f5cd1a78aae32384551c74e6c19304 removed filtering
of annotations when there was a selection alongside other changes.

This re-introduces the check to see whether there is a
selection and if so whether an annotation is in the selected
set when determining whether to show a thread.

Fixes #2553

Implement focus on a group

Fix icon fonts in production builds

The stream page was broken - showing only annotations from the group
that was focused the last time the user was using the sidebar.

Fix it to show annotations from all groups.

When switching between groups (and reloading the angular view more
generally) drafts are persisted. But we don't want to display drafts for
groups other than the one currently focused, because otherwise we'll end
up in a position where we can see annotations published to another
group.

This commit adds an additional condition to
`ThreadController#shouldShow`: if the thread root annotation has a group
set, and that group doesn't match the focused group id, then the thread
will be hidden.

Always focus the Public / __world__ group if the groups feature is
toggled off.

When the groups feature was off a group other than Public might have
been retrieved from the browser's localStorage (this could only happen
if the groups feature had previously been on for the user) and the wrong
annotations would be shown in the sidebar.

Replace `isSidebar`, `isEmbedded`, `annotation-embedded`, `annotationEmbedded`
and `embedded` with a single `isSidebar` variable.

- Rename `isEmbedded` in AppController to `isSidebar`.

- Rename `embedded` in AnnotationController to `isSidebar`, it just passes the
value of `AppController`'s `isSidebar` into `annotation.html`.

- Rename the `annotation-embedded`/`annotationEmbedded` variable that is used
to pass `isSidebar` (was `isEmbedded`) into `AnnotationController`,
rename it to `is-sidebar` / `isSidebar`.

- Delete the duplicate `isSidebar` variable from `WidgetController`'s scope,
`WidgetController`'s templates can simply access `AppController`'s `isSidebar`
from the scope.

Note that there's another variable, `isStream`, that's actually true when we're
either in the sidebar or on the stream page, but not when we're on individual
annotation pages. This is used to show/hide the
"Sorted by newest, oldest, location" menu which appears in the sidebar or
stream but not on individual annotation pages (the "location" option in this
menu only appears when in the sidebar not on the stream).

This commit leaves the `isStream` variable alone.

So the `isSidebar` variable is now used to show/hide the following elements:

- The share dialog (share this page on twitter etc) is shown in the top bar,
only when in the sidebar (and not on the `/stream` page or on individual
annotation pages).

- The group list dropdown menu, shown in the top bar only when in the sidebar.

- The "location" entry in the sort menu (sorted by newest, oldest, location)
shown only when in the sidebar.

- The "citation" on annotations that says which page was annotated
(the 'on "Example Document" (example.com)' in the annotation's title),
is shown only when _not_ in the sidebar.

When a user clicks on a group name in the "scope selector" dropdown
menu, we want to filter the visible annotations by group. This commit
implements a rather inefficient but functional approach to this, simply
reloading the angular view.

In addition, we make sure that the initial annotation load includes a
filter on the currently-focused group, and we discard non-focused-group
annotations coming in over the websocket.

Avoid String.prototype.startsWith() for compatibility Safari and IE

Links to source document URIs were broken under Safari <= 8 and
other browsers as well due to reliance on the
String.prototype.startsWith() API

This issue went unnoticed in Karma/PhantomJS tests because
Karma was primed with the complete set of polyfills from
the js-polyfills library, including many (all?) ES6 polyfills.

This same set of polyfills was_not_ used in the browser build however.

This commit fixes the original issue by using 'indexOf()' instead of
'startsWith()' and reduces the likelihood of such problems going
unnoticed during testing by using a much more minimal set of polyfills
under PhantomJS.

The alternative approach would be to go in the opposite direction
and polyfill any ES6 APIs in the browser. However, we need to be
careful about code bloat, so the approach taken here is the more
conservative option.

Fixes #2568

Show filenames of local documents with titles

As described in GH #2571, URL rebasing is broken
in the CSS asset pipeline, so relative URLs in
CSS files under styles/vendor are incorrect.

Previously icomoon.css worked because one of the
font variants (TTF) was inlined as a data URL.
This broken in the previous update which had only
the relative .woff URL.

This commit patches the issue by using an absolute URL
in the icomoon.css file. It will be fixed properly in
the CSS build as part of moving that out of the Python
web app.

See #2571

When the annotated document is a local (file://) document and it has a
title, then show the filename in place of the domain on the annotation
card. For example:

  seanh on "Document Title" (filename.pdf)

In cases where the document has no title then the filename would already
have been used in place of "Document Title" so don't repeat it in
(...)'s.

For remote documents the domain name is shown in (...)'s instead and the
document title is hyperlinked so the people can see the full URL by
hovering over the link.

Consolidate thread show/hide logic into ThreadController

This template conditional is notorious for accumulating extra terms, so
this commit rolls it into ThreadController where it can be more easily
tested.

T89 combined scope save btn

When changing permissions via the dropdown menu,
the changed permissions were applied to the _domain model_
representing the saved annotation instead of the _view model_
representing the current annotation being edited.

The change to the domain model triggered a reset of the view
model via AnnotationController.render(), losing any unsaved edits.

This commit makes AnnotationController.setPrivacy() apply permissions
changes to the view model in the same way as other edits in the
annotation view. These then only take effect when the 'Post to'
button is clicked.

Fixes #2567