Selection and adder-related fixes

 * Update Annotator to bbad33fe (typed-packaging branch),
   which has some adder-related tweaks/fixes.
   (More sane encapsulation of the `canAnnotate` behavior,
   following suggestions from @gergely-ujvari)
 * Copy Annotator's changes to our overrides:
   * In `onAdderClick()`, set `inAdderClick`
   * In `onSuccessfulSelection()`, return false when annotating is forbidden
 * Upon building the channels between the guest and sidebar,
   synchronize the enableAnnotating state.

Really fixes #949.