Prevent annotation attempts when not signed in

Simply hides the annotation form--which implied you could
use the thing...--and instead tells the user to sign in,
so they can do what they came to do.

s/viewable/visible/

Proper feature flags

Our first attempt at integrating feature flags with the frontend
required a rebuild and redeploy of the extension, which somewhat
defeats the purpose of feature flags. This commit wires up the new
feature client introduced in the preceding commits, allowing feature
toggles to update behaviour of already-deployed clients.

In order to respond to feature flag changes on the frontend, we need a
way of knowing what the current feature flag values are on the backend.

This commit adds a basic feature flag client that retrieves current
feature flag values by making an ajax request to the server. The client
also includes a cache, and supports retrieving new value from the server
when the cache expires.

Thread collapsing redux

Since there is no username, collapsing a draft when not signed in
had been causing the annotation to disappear completely. Now, there
is a clear prompt that holds the space.

Make the tags section use .annotation-body (because tags are a form of
body) and put the form actions, reply count, and license messages into
the footer so that these collpasing properly and uniformly.

This reverts commit 561544e4d289e728035aa9b549758b3b55d281f0.

This reverts commit 0c6bd1b36e234c43cfdb15edac1d06792c6f259a, reversing
changes made to 0ffdda5d6d144d184348574ada953354100788c6.

Be slightly more defensive when processing annotations for the atom feed.

Expand the search API docs

Improve thread collapsing UX.

- Keep the namespaced classes sorted by file
- Keep the collapsed annotation overrides in the annotation file
- Improve the vertical alignment of the timestamp better
- Make margins and elements go away in the collapsed state rather
  than using negative margins to hide them
- Simplify the thread expander styles

Topbar toolbar harmony

Fix guest embedding

To prevent an Annotator is undefined error, the constructor class is set
by the object returned from the hypothesisConfig function. The documentation
has also been updated.

When the search icon is clicked give focus to the search input.

Harmonize the styles of the buttons in the top bar and the toolbar.

- Match font size of icons at 18px
- Buttons are .btn-clean and have minimum width so icons are square
- Transitions for background color
- Simplify the styles for the top bar, using the newly consistent
  clean top bar button styles instead of specific styles for the
  share button.

- Threads collapse to single lines.
- Use iconograpy consistent with collapsing / expanding UI in other
applications
- Threads are fully expanded when you click replies on a top level annotation.
- Delete old test and add new tests.

Add ability to share via links from the sidebar.

Use of {{angular templates}} causes problems on pages with Annotator
enabled due to Annotator's habit of splitting text nodes whenever you
select anything. Specifically -- if you select one of the words in this
text and then change the privacy setting, it will end up rendering as
something like

   PubliOnly Me
   Only Melic

or similar. Using a span tag and ng-bind is a bit of a hack but it
prevents this from happening.

Oh, Angular...

Make annotation visibility level more explicit

- Private annotations have the word private as well as the lock icon on the card
- Small styling refinements have been added to make the annotation-license
- Show the word private alongside lock icon.
- Show message explain visibility setting when editing.

Small ux improvements

- Use document plugin to get canonical url for sharing.
- Introduce Topbar share icon
- Add social media icons to icomoon
- Generate via uri in the share-dialog directive
- Add sharing via Facebook, Twitter, Google plus, and email
- Make account dialog and share dialog consistent
- Add information about sharing to the help page.
- Add tests (Thanks @nickstenning!)

Report form level errors

When we call `form.validate()` and the validation fails, the raised
exception is a `deform.ValidationFailure`. This object has an `error`
attribute which represents the underlying validation error object for
the entire form.

Previously, if the validation failure were a result of top-level
validation errors (such as the fact that an unactivated user is trying
to log in), this error would be lost, because we only reported errors
for the forms fields, or "children".

This commit changes `h.accounts.views.validate_form` so that it converts
the entire `colander.Invalid` object into a dictionary using its
`asdict()` instance method. By doing this, we get two immediate
benefits:

- top-level validation errors are reported in the '' (empty string)
  field
- we avoid the need to aggregate form field errors by hand in ajax_form

In addition, we need to deal with this case on the frontend, so this
commit also changes the formRespond directive so that if no overall
"reason" is provided for failure, then an empty-string member of the
"errors" object can set the overall validation status (and error
message) for the form.

Refactor search

Ask for "Username or email address" when logging in