Keyguard bouncer notifications; focus moving and the bouncer; slops

Integrate changes from prototype app

* Add callbacks for bouncer state changes

* Dismiss the bouncer if focus leaves the challenge area

* Increase edge swipe region, treat this as a slop for
  SlidingChallengeLayout's drag handle. (This allows edge swipes in
  the drag handle area to still page widgets instead.)

Change-Id: I732de1a8d999a34c7cc8aa8ed99e24b597f3444c