Update QS tile states after unlocking

So the visibility state is up-to-date when we do a two-finger
expansion gesture, so the height is correct. Also fixes flickering
when overscrolling the initial panel expansion.

Also set thread priority of QS handler thread to background priority,
so it doesn't eat away precious cycles during animations.

Bug: 18183633
Change-Id: I0609509484582d82f0dc307eb2535bc3711b30e3