Settings: read keyguard package name from overlays

Change-Id: Ief4750c91aa22c2033d31aacfea4cfbe245d61a8
Signed-off-by: Roman Birg <roman@cyngn.com>

Conflicts:
	src/com/android/settings/cyanogenmod/LockscreenButtons.java
	src/com/android/settings/cyanogenmod/LockscreenInterface.java
Device settings: Add needed fragment and  proguard flag