systemui: Dejank the navbar

 * In order to maintain that high-performance feel, the navbar
   button glow animation must be smooth.
 * Custom button handling and suboptimal haptics implementations
   have made it quite bad in CM. Press recents fast and it will
   immediately become the bane of your existence.
 * Post a runnable to setup and play these animations on key up/down
   to eliminate the jank.

 * There is still latency in the input path, which is seen on hard
   keys. This is not addressed here.

Change-Id: I537318b680f401edce3fbd42ed5a5ae2ba57a067