Framework: Add Home/Back buttons available for rebinding (1/2)

Finally, we can disable or rebind all hardware buttons!
Also adds Expanded desktop toggle and Notification shade toggle

Change-Id: I0ca51c25e8434696a514fd1ef1e1e33543bf066a

Conflicts:
	core/java/android/provider/Settings.java
	policy/src/com/android/internal/policy/impl/PhoneWindowManager.java