Add YAPF config and docs for automatic formatting of Python source code

Double the truncation threshold height for annotations

Prevent double-posting of new annotations

As per https://trello.com/c/7QtpfMB5/ increase the threshold
so that only very long annotation bodies are truncated.

When the user clicks the 'Post' button to create an annotation,
optimistically switch the card back to View mode but display
a 'Saving...' indicator in place of the Reply/Edit/Delete links.

This makes the UI appear more responsive when the user clicks
the Post button and also prevents an issue where the user could
click 'Post' multiple times during the save and create multiple
annotations.

 * Fix a possible inconsistency between the 'Post' button's enabled
   state and whether or not the save() function can succeed.

   The hasContent() and isShared() methods also already have tests,
   so this lets us remove several redundant tests.

 * Fix inconsistency in the return type of the save() function -
   always return a promise.

 * Treat negative status values as network errors as well as 0.
   If the server is unreachable, the real status value may be -1.

Fixes #2864

Decouple sidebar app HTML / embed JS template rendering from Pyramid

Don't open "welcome page" when installed by admin policy

Decouple the Hypothesis service URL from the app's base URI

Make these links work when the app is hosted at a different
base URL from the Hypothesis service.

Make these links work when the app is hosted at a different
base URL from the Hypothesis service.

When the Share dialog is hosted in the Chrome extension
and the <base> URI is not set to point to the Hypothesis service,
the share links need to have a scheme set explicitly.

Remove the assumption in the sign-in menu that the
baseURI for the page is the same as the Hypothesis service.

Also use controllerAs and bindToController for consistency
with recently updated directives.

Previously the 'New Groups' link opened '/groups/new' in a new
window, which only worked if <base> URL matched the URL
of the Hypothesis service. Instead explicitly use
the serviceUrl from settings.

Also remove an empty set of tests for the group list controller.
The tests are now all done at the directive level.

Previously the URL set as the <base> tag was used indirectly
to specify the URL of the Hypothesis service that various
links referred to.

Make things clearer by adding an explicit 'serviceUrl' attribute
to the Hypothesis client settings and use that in place of the
baseURI.

The custom template whitelist configuration has been removed
because all of the templates are embedded in app.html, so the
default value of ['self'], allowing templates to be loaded
only from the same domain as the page, is fine.

Fix canceling edits reverting to the first-loaded version of an annotation

Extract the login form into its own directive

This makes the login form consistent with other recently
written components by having the controller and directive in a single
file and using an element directive in the main app.

Only show the 'Create Account' banner in the sidebar

Recognize 'group' as a valid parameter name in search queries

Remove the static blocklist

The configuration option for defining a static blocklist of sites
on which Hypothesis should not load has never been used and
we're not anticipating doing so.

Remove the incomplete Firefox extension

A recent successful prototype of a Firefox extension
based on the new WebExtensions API highlighted that as
the way forwards for Hypothesis on Firefox, as it lets
us offer feature parity with much easier maintenance.

If we decide that we want to support the extension for Firefox pre-45, we may
do that by shimming the Chrome APIs using the JPM SDK APIs, similar
to what https://github.com/einaregilsson/Redirector have done.

This commit removes the legacy incomplete
Firefox extension which is missing all of the recent improvements
and tests for the Chrome extension.

Move configuration of ES index into search

Use raven-js for client-side error capture and reporting

When updating an annotation, the update is currently applied
to a copy of the domain model. AIUI the rationale for this is to ensure
that 'domainModel' always reflects what is actually stored on the
server, so it should not be updated until after the update is
successfully committed.

However, after the update is successfully commited, the view was
updated with the updated domain model, but the local domain model
instance was never replaced. Therefore when reverting changes,
the card reverted to the first-loaded text for the annotation
instead of the last-saved version.

This commit fixes the problem by replacing the domain model
reference whenever an annotation update is received.

Fixes #2875

The backend already supports searches for 'group:hashid' but
this was not supported on the stream because 'group'
was not recognized as a valid parameter so it was passed
to the backend in the 'any' field.

For browsers that support it (currently only Chrome >= 49),
catch unhandled promise rejections and report them to Sentry.

This also fixes an issue with incorrect subclassing of
the base Error type in errors.js

Strip Via prefixes in URL normalization

Add a small hysteresis threshold for annotation quotes

If an annotation quote requires 2 or 3 lines of text, it will
not be truncated, otherwise it will be truncated to 2 lines.

Capture exceptions reported via Angular's $exceptionHandler
service and window.onerror and report them via Raven.

The client currently uses the same Sentry DSN as the main
application, which gets the DSN from the SENTRY_DSN
environment variable.

 * Add a <script> tag to all pages on the site which
   defines a window.RAVEN_CONFIG variable which provides the DSN
   and release string needed to configure Raven JS on the client

 * Configure and setup RavenJS in the main site JS, Chrome
   extension and the sidebar.

   For the sidebar, Angular integration is configured
   using Raven's Angular plugin.

 * Configure the user ID associated with Sentry reports
   when the session state is received

 * Extract the code which builds the sidebar/extension
   config dictionary out of the template into
   its own module for easier sharing between the Chrome
   extension and the sidebar's code.

Implement a hysteresis threshold in excerpts

Allow the excerpt's contents to exceed the collapsed
height by a threshold set with the 'overflow-hystersis' attribute
before the excerpt's contents are truncated.

This fixes a problem where the contents of an annotation
body could exceed the threshold by only a couple of pixels,
resulting in a 'More' link which resulted in only half a line
of extra text being revealed.

Fix annotation thread collapsing

This makes it possible to unit test it easily