LockScreen: Option to hide initial page hints (1/2)

This will add an option to hide the initial page hints
that are shown left and right when the device is turned on.

Change-Id: Id4f29f7cfbaca6b4dd91f0b2de2b8195a966259b
Signed-off-by: Dirk Rettschlag <dirk.rettschlag@gmail.com>
Add some xhdpi drawables needed for that UI Mode commit

Change-Id: I7b1be716501107ca121aa53ed899b40d1770d9ef