Adds ability to answer call with hardware HOME button (preparation to winter time)

Patch set 1 : Upload the change
Patch set 2 : Only change the real Author
Patch set 3 : Bugfix:
              Add register for the ContentObserver (Settings.Secure.RING_HOME_BUTTON_BEHAVIOR) in PhoneWindowManager,
              and correcting the logging functions and deleting some unneeded comments
Patch set 4 : Rebased

Change-Id: Ia2aba658ca628232d8e283219950528b60eced4a