When visiting a direct-linked annotation (ie. #annotations:<id> is
present in the URL) we want to preserve the selection when the user
signs in, whether the annotation was private or in a group, in which
case they will need to sign in to see it, or public, in which case they
might need to sign in to reply.

Previously public direct-linked annotations became deselected when
signing in because they were unloaded when switching accounts, and this
fired the same ANNOTATION_DELETED event as when an annotation is
removed, which results in the annotation being removed from the
selection.

This commit enables the selection to be preserved by introducing a
different event within the app when annotations are unloaded vs.
deleted. When an annotation is unloaded, it is not removed from the
selection.