The `BEFORE_ANNOTATION_CREATED` event was used for two purposes:

 1. Invoke `annotationsService.create(...)` to create the annotation in
    the sidebar.
 2. Scroll the newly created annotation into view

Resolve (1) by calling `annotationsService.create` directly from the
`frameSync` service and resolve (2) by watching for changes to
`unsavedAnnotations()` in the store and scrolling to the new annotation
when it appears.

There is one functional change which is that replies will be scrolled
into view, as this seems like a useful behavior if the user clicks the
"Reply" button for a thread and the input field appears below the bottom
of the screen.