QS: Wire up screen casting to tile/panel.

Use MediaProjectionManager to determine whether or not
screencasting is active, when it changes, and to stop
casting.

Also:
 - Implement hashCode/equals on MediaProjectionInfo
 - Fix unintentional recursion in the service.

Bug:16488053
Change-Id: Icd1a88f23bbdf1d4c1915b30cb2508f8fe9d6d7e