DeskClock: Avoid DeskClock layout displays abnormally on landscape.

- ConfigChanges property for DeskClock activity won't let the activity
recreate and re-layout when rotating the device.
- Delete the activity property. Meanwhile, when the activity recreate
it will reset music seletion source to be zero which lead to the music
picker uri null. Save and restore the seletion before re-createing.

Change-Id: If680f0b262231cf3b8b7186c9dbacea7c0d1574e
CRs-Fixed: 655098