Fix default values for settings not being used in the browser extension

The logic for skipping host page configuration of settings that are
ignored by the browser extension did not take into account any default
values configured via the `defaultValue` property.

Also fix and add several related tests:

 - Correct the test that checks behavior when `defaultValue` is not set
   to use `undefined` rather than `null` to indicate a missing
   `defaultValue`.

 - Add test case for when a default value is overridden.

 - Add test case for default values in browser extensions.

Add config option to display a clean onboarding look to users.

 - Use a variable instead of a hardcoded color for the "New note" button
   in the sidebar tutorial.
 - Remove unused `width` and `height` attributes. The icon's size is set
   via `width` and `height` properties in CSS.

See https://github.com/hypothesis/product-backlog/issues/351

Remove orphans tab feature flag checks

Show display names for eLife only

Whenever possible, always show display names instead of usernames on
annotation cards if the creator of the card is a third-party user.

Even if the client_display_names feature flag is turned off, display
names _will_ still be shown for third-party users.

Display names will _not_ be shown for first-party users, unless the
client_display_names feature flag is on.

If the api_render_user_info feature flag is turned off in h, or if the
user doesn't have a display name, then of course the username must be
shown as the client has no access to a display name.

In a future commit annotation-header.js is going to make use of
isThirdPartyUser() to add a new behavior.

In a future commit some individual unit tests are going to need to
change fakePersona's behaviour, so they're going to need access to it.

fakePersona is reset between tests in a beforeEach(), so individual test
functions changing its behaviour will not affect other test functions.

These get printed out if something errors in a beforeEach(), making it
easier to find the error. They also help to make the code easier to
read.

I don't want the tests for annotation-header.js to be calling the real
persona.js. This isn't good test isolation, and it makes it more
difficult for future tests I intend to write to change persona.js's
return values, without tightly coupling those tests to implementation
details of persona.js.

Only show display names on annotation cards if the client_display_names
feature flag is on.

The api_render_user_info feature flag also needs to be on in h,
otherwise the client won't receive any display name from h.

The user also has to have a display name set in h.

If any of these three tests fail then fall back to showing the username.

This doesn't change the behaviour of either of the tests in any
significant way.

Future commits are going to be adding a lot more cases to this
parametrize-style test.

This is now always set to true following the removal of the
`orphans_tab` feature flag checks.

This has been enabled for all users for many months now.

Add config option to enable the new note button when the notes tab is selected.

Re-arrange OAuth service tests

Move the tests for fetching and persistence of tokens from/to storage
into the `describe('#tokenGetter', ...` block since this is the method
called from outside the service that initiates the fetching /
persistence.

Also reword a couple of the test cases to be clearer now that the OAuth
service now handles fetching tokens using methods other than exchanging
grant tokens.

Change UI for Elife.

See https://github.com/hypothesis/product-backlog/issues/350

Add config options for the following:

disableToolbarCloseBtn: false/true
Disables and hides the close button on the toolbar

disableToolbarMinimizeBtn: true/false
Disables and hides the minimize button on the toolbar

disableToolbarHighlightsBtn: true/false
Disables and hides the highlights button on the toolbar

disableToolbarNewNoteBtn: true/false
Disables and hides the new note button on the toolbar

disableBucketBar: true/false
Disables and hides the bucket bar

enableSidebarDropShadow: true/false
Turns on the dropshadow for the sidebar

theme: 'clean'
Turns on the 'clean' theme for the sidebar. By default the classic view(with annotation cards) is turned on, which the rest of the Hypothesis users will see.

usernameUrl: 'someurl/'
The url to direct a user to when their username in the annotation is clicked.

Remove form-input and form-validate directives

Coalesce anchoring status updates

Respond to CR feedback that the function of this code was unclear.

Profiling the test case in #556 showed significant overhead from the
processing involved in or triggered by each `UPDATE_ANCHOR_STATUS`
action handled by the store. Previously one `UPDATE_ANCHOR_STATUS`
action was dispatched for each annotation whose anchoring status
changed.

Improve the situation by making the `UPDATE_ANCHOR_STATUS` action handle
updates for multiple annotations at once and modifying the `frameSync`
service to coalesce anchoring status updates from the host page into
a smaller number of `UPDATE_ANCHOR_STATUS` actions.

Fixes #556

Historically annotations did not have local tags until after they had
been anchored in the page.

This is no longer the case as annotations are assigned local tags as
soon as they are added into the app state by ADD_ANNOTATIONS.

Therefore, it is no longer necessary for the UPDATE_ANCHOR_STATUS action
to support updating the tags of annotations or to support identifying
the annotation which has been anchored by its ID instead of its tag.