Properly laying out FaceLock on lockscreen

- FaceLock area now specified in layout files instead of trying to
  grab an existing view, which was only practical if pattern was
  backup method

- Now fills area it is supposed to and works with pin as well as
  pattern backup

- Backup method is no longer exposed behind FaceLock just before it
  starts or just after it tells the lockscreen to unlock

- Added synchronized blocks so FaceLock cannot be told to stopUI by
  two different threads at the same time

Change-Id: I3bfad6b44dbe0e3c2ea3c87d2978451c22a7484c