input: Wake on navigation button

Take #3 at this infernal feature.

 - Create a new policy interceptNavigationButtonBeforeQueueing which
   sends the event to the window manager when the screen is off and the
   key is down.
 - Remove previous code which only worked for devices that treated this
   as a keypress.
 - Remove some dead code in the window manager for music-skipping which
   is no longer used by CM

Change-Id: I953095884e4848c3cde2de7b6ab301ee5128699b