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.

Flagging or unflagging an annotation previously updated the status
flag indicating whether an annotation had been flagged by the current
user but did not update the flag count if the user was also a moderator.

This needs to be done to make the moderation banner's state update when
a user who is also a moderator flags an annotation.

Tests for actions should live in the test module associated with the
module that defines the actions.

Use correct case for `flagCount` key

This property is camelCased rather than snake_cased in the annotation
response from the service.

Enable first-party users to flag annotations

Update moderation API use

Enable first-party users to flag annotations if the `flag_action`
feature flag is enabled for them.

Move the flag count to a helper which is easier to test and re-use.

The `hidden` state has been moved from the `annotation.moderation` key
to a top-level property of the annotation.

The previous code was incorrect because depending on the failure, the
error might not be an `Error`. This needs to be fixed in the API client
but for the moment, sidestep the problem by just displaying a fixed
string.

Moderation state was originally going to be retrieved via a separate API
call from /api/search but is now returned as a `moderation` field in the
annotation response.

This commit removes the separate `moderation` state from the Redux
store.

In the `<moderation-banner>` and `<annotation>` components, read the
moderation state from the annotation object instead of fetching it from
the app state.

After an annotation has been hidden or unhidden by a moderator, the
moderation state needs to be updated locally to reflect the change.

The `hide` API has now been implemented on the server. The `unhide` API
has been agreed but not yet implemented.

Adding branding config docs

Change "when it is being save" to "when it is being viewed" to avoid
implying that it might only apply while changes are being saved to the
server.

Show the flagged status for annotations that user has flagged.