Quick settings bug fixes.

 - Fix issue where notifications were positioned offscreen after
   quick screen toggle.
 - Better QS scrim hiding, use existing layout transition.
 - Don't allow a reposition if the settings animation is currently
   running.
 - Delay chevron animation during toggle to avoid drawing over each
   other.
 - Keep the screen on while the user is poking around with QS on
   the keyguard.
 - Cap the QS expansion to the bottom of the status view on keyguard.

Change-Id: Ib63874d0c6a33db81923080f25cb8f208e614faf