add Custom Lockscreen switch

Change-Id: Icb96b85fb7ecf1b6716627f96f393f1fc9da09df

Conflicts:
	res/xml/lockscreen_interface_settings.xml
	src/com/android/settings/cyanogenmod/LockscreenInterface.java

Conflicts:
	src/com/android/settings/cyanogenmod/LockscreenInterface.java