Remove the need to alias the `Adder` instance to `self` by using
arrow-functions.

This commit and the next few refactor `Adder` to a "proper" class for
easier readability.

Add `expand` param to all groups.list requests

Minor bug fix

Move date, time & retry utility code to `util/` dir

Pdf subframe annotation

As per #648, move several modules containing utility functions which
have no dependencies on other code to `src/sidebar/util`.

Rename "annotationUI" => "store"

Rename the fake/stub implementations of the Redux store used in various
component and service tests.

Update the name of the identifier used for the Redux store in various
contexts, following the previous refactoring to move store-related code
into `store/`.

Move Redux modules and entry point to `store/` directory

Changed background to selected element in PDF.js to visualize the searched content

Remove reference to `group.url`

Remove `group.public` property from annotation component

Update icon for restricted groups in publish-annotation-button

Move away from `public` property in application components

Keep the structure of having modules at higher layers (ie. with more
transitive dependencies) in the app nearer the top of the list by moving
the store registration to the bottom.

Following the plan outlined in #687, restructure the Redux store as
follows:

 - Move the entry point from `services/annotation-ui.js` to `store/index.js`
 - Move the modules which define bundles of reducers, action creators
   and selectors to `store/modules/{module-name}.js`
 - Move related utility code to `store/{module-name}.js`