Render "censored text" for hidden annotations

Fix variance in annotation share dialog test coverage

Rewrite and simplify the permissions service

Display a column of horizontal stripes to give the impression of
censored text for hidden annotations if the annotation's content has
been removed by the service.

Implements mock at https://github.com/hypothesis/product-backlog/issues/231#issuecomment-295600762

Remove a broken unit test

Git push to hardcoded https URL and master branch

As noted in this comment:

https://github.com/hypothesis/client/pull/356#discussion_r111998459

this test doesn't actually test what it says it does, and fixing the
test would require some refactoring of the code under test. For now,
just delete the test.

Change the `git push` command that the `npm version minor` command runs
when doing a client release to:

1. Hardcode the https URL of the client repo, instead of assuming the
   user's `origin` is set to it

2. Push only the user's master branch to the remote master branch
   (instead of potentially pushing other local branches as well)

Use the new `/api/links` resource

There's no unit test for this. Because of Promises, it cannot be tested
without refactoring serviceUrl.

Change serviceUrl to return URLs by expanding URL templates received
from h's /api/links resource, rather than using hardcoded URL templates
as it previously did.

The interface and contract that serviceUrl presents to its users remains
the same - the fact it's now sending an API request to get the URL
templates, and waiting for the response, is completely hidden from its
users.

This hiding is achieved by two tricks:

1. Always returning "" for an expanded URL if the API response hasn't
   been received yet, rather than, for example, changing the interface
   to return Promises instead of strings (which would then require
   changes to every user of the interface, and possibly their users...)

2. Updating annotationUI, the Redux state store, with the new URL
   templates when the API response is received. This causes any
   AngularJS components that might have used an (empty string) URL to be
   re-rendered, they will call sericeUrl URL again and this time get the
   actual URLs.

   This is completely transparent to the components - annotationUI
   causes AngularJS to call them again and this time they will get a
   different result from serviceUrl. The code of the components
   themselves doesn't need to change.

Additionally, serviceUrl will never throw errors if it hasn't received
the API response yet. For example there is no error if an unknown link
name is requested, or if unused template params are given. It just
always returns "". Once it _does_ have the API response then it will
start throwing errors for bad requests, the same as it did previously.

Add a new function to `store`, the https://hypothes.is/api wrapper,
that provides access to the new https://hypothes.is/api/links resource.

Add a Redux reducer for storing the links (URL templates) from the
/api/links HTTP resource in the state store.

This adds a missing test for the behavior and also fixes variance in
test coverage between runs because the code that implements this
behavior sometimes ran and sometimes did not.

Instead of adding event listeners to the document to track clicks
outside the share dialog, use a transparent backdrop element behind the
share dialog which covers the whole page.

This avoids the need to register/unregister document-level event
handlers in the controller, removing some code which was untested.

Refactor the annotation share dialog's controller for consistency with
other components:

 - Move controller to a top-level function in the file

 - Capture `this` as `self` rather than using `bind`

 - Attach `onShareClick` to controller rather than `$scope`

This commit replaces the 'permissions' service with a minimal
implementation which supports only what is required by the
actual permissions model in the client and service, rather than
all the possible permissions implied by the structure of the
`permissions` field.

In the client and service, annotations are simply "shared" or "private":

 "private" annotations can be read, updated and deleted only by
 their creator.

 "shared" annotations can additionally be read by everyone in the group
 that the annotation is associated with.

Update flag count after moderator flags an annotation themselves

Only display CC 0 license for shared annotations in public groups

Do not display the CC 0 license for annotations that are shared in a
private group.

Simplify handling of quotes in annotations

Although annotations can contain multiple targets in theory, in practice
we only ever store one target per annotation and one quote selector per
target.

Until we have a clear use case for associating multiple quotes with an
annotation, we can simplify the code by only rendering the first one.

Extract annotation action buttons into a separate component

This refactors a bunch of markup that was duplicated for each action
button and should make it easier to add tests specifically for the
button's behaviors in future.

 * Create an `<annotation-action-button>` component and move existing
   markup for buttons there.

 * Refactor `<annotation>` test to use the same set of bindings for
   the mock `<markdown>` component as the real one.

Extract annotation header into a separate component

The `<annotation>` component is growing large and unwieldy, especially
the tests. As a first step to making it easier to follow, extract the
header (which displays username, timestamp, document metadata and group
name) into a separate component.

Use hyphens instead of underscores in template filenames

The use of underscores dates back to when the templates were part of the
service code and used the same naming conventions as the service's
Jinja2 templates.

Using hyphens makes the template filenames match the other files
which make up a component (JS & SCSS files). This makes it easier to
switch between the different parts when using a fuzzy file finder.