Lockscreen: added option for custom unlock target
Allows to set unlock target manually to any target available. GravityBox
Unlock action has been introduced for this purpose.
Conflicts:
	res/xml/gravitybox.xml
	src/com/ceco/gm2/gravitybox/ModLockscreen.java
	src/com/ceco/gm2/gravitybox/preference/AppPickerPreference.java
	src/com/ceco/gm2/gravitybox/shortcuts/ShortcutActivity.java