R1:5d7202526f3d

Hide the Differential keyboard focus reticle after Quicksand navigation

Summary: Ref T8047. Ref T12634. When we sleep, hide the reticle. Restore it when we wake.

Test Plan:
- With Quicksand enabled..
- Used "j" to select a change in a revision.
- Navigated away by clicking a link.
- WOW! Reticle vanished properly!
- Used "back" to return.
- Reticle returned properly.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T12634, T8047

Differential Revision: https://secure.phabricator.