Add HTML baseline tests

Add a set of baseline tests for HTML anchoring which attempt to anchor a
set of selectors for an annotation using data in the format returned by
the Hypothesis API and then verify that the same selectors are generated
when re-describing the anchored ranges.

Remove 'defer_realtime_updates' feature flagging

This is now enabled by for everyone, so we don't need the feature flag
any more.

When anchoring many annotations on a PDF, the text of the same page may
be requested many times.

The text is initially fetched via an async call to
PDFViewerApplication.pdfViewer.getPageTextContent() and the result is
then cached for future use.

Previously the cache was only updated once this expensive call
returned a result. Consequently when anchoring many annotations at once,
there would be a lot of unnecessary cache misses and repeated calls to
PDFViewerApplication.pdfViewer.getPageTextContent()

Fix the problem by storing a promise for the result in the cache when
the text for a given page is requested the first time. Consequently the
text for each page will only be fetched once.

Added links to help center from help panel

Fix Jenkins builds failing if package.json or shrinkwrap change after branch is initially pushed

This fixes a couple of incorrect usages of Sinon assertions which
resulted in test failures with the latest patch version of Sinon.

 * assert.calledOnce() only takes one argument

 * Sinon assertions do not take a message argument as Chai assertions
   do. See http://sinonjs.org/docs/#assertions

* Move event handlers out of AnnotationUISync

As a step towards having all bridge event handlers in one place, move
these event handlers into frameSync.

 * Add tests for findIDsForTags() and for re-exporting of this
   function from annotationUI

* Move sidebarOpened event handler to FrameSync service

* Remove the AnnotationUISync service

Its functionality has now been moved into the FrameSync service, except
for the logic that was intended to synchronize the "Show Annotation
Highlights" logic across multiple frames, since this is clearly broken
[1].

The two pieces of functionality related to this we need to support at
the moment are:

 1. The `showHighlights` config option to set whether highlights are
    initially visible.

 2. The highlight toggle button in the sidebar's outer frame

Both of these work without the sidebar app's involvement.

[1] See https://github.com/hypothesis/h/issues/3433 and
    https://github.com/hypothesis/h/pull/3295

Jenkins is currently configured to re-use workspaces between builds of
the same branch. Run `make clean` at the start of the build to ensure
that any artefacts from the previous build of the branch are removed.

With the following steps, the second invocation of `make` should trigger
installation of npm dependencies:

 1. Run `make`
 2. Edit dependencies in `package.json`
 3. Run `make` again

The shrinkwrap was not updated when `requests` was updated from v2.71.0
to v2.72.0.

Fix normalization of ranges that start at an element node with no children

This isn't needed since we're not translating error messages.

Rename the `$$tag` annotation property to `$tag`.

The range normalization code failed to take account of ranges where the
start container was an empty element with no children.

Fixes #73

Replace the Range functions from the compiled version of Annotator 1.2.x
with the latest CoffeeScript source from the v1.2.x branch of Annotator,
plus the fix added in b3056d27

This includes fixes for BrowserRange#normalize from
https://github.com/openannotation/annotator/commit/9bec776511a717ef944b36ed7cca3d107bd95c88

In addition, this removes the dependency on the Annotator framework from
annotator/anchoring and the highlighter, getting us closer to a point
where we can remove the dependency of the annotation layer on Annotator.

Fixes #109

Adding code coverage reporting to Karma tests

This property previously had a "$$" prefix instead of the conventional
single "$" prefix for local-only properties of annotations for
historical reasons.

This is a followup PR to:
https://github.com/hypothesis/client/pull/126

* Rename the annotation property storing the local tag to `$tag`

This property previously had a "$$" prefix instead of the conventional
single "$" prefix for local-only properties of annotations for
historical reasons.

* Remove explicit copying of the `$tag` property in Object.assign() calls

The `$tag` property is now enumerable.

Update proxyquire

Fallback to last text node when we will fall into a null sibling node situation

Add PDF anchoring unit tests

Add a set of tests using a fake implementation of PDF.js'
PDFViewerApplication interface.

The initial set of tests simulate a nice born-digital PDF in which the
text layer of the PDF contains one <div> per line. In future we can
easily extend this to emulate the kind of structure that would be seen
when working with eg. an OCR-ed PDF

Update this dependency in preparation for updating the
dom-anchor-text-{quote, position} libraries.

The previous version indirectly used an old version of
combine-source-map that is not compatible with the inline source maps in
the newest versions of the dom-anchor-* libraries.

Remove the "-app" suffix from Gulp tasks

Remove AnnotationUIController

This is a holdover from when the Hypothesis service front-end and client
application lived in the same repository and the "-app" suffix was used
to indicate client-specific tasks. Removing this gives the tasks more
obvious names - "build", "build-js", "test" etc.

All of the functionality in this module is either unused or duplicated
elsewhere:

 * The $scope.{selectedAnnotations, focusedAnnotations,
   selectedAnnotationsCount} properties were unused.

   Note that there is a very similarly named `selectedAnnotationCount`
   scope property defined in `WidgetController` which _is_ used

 * The ANNOTATION_DELETED event handler duplicated another one in
   root-thread.js

This function expects an ID, not an Annotation