Improve motion for wake-and-unlocking while pulsing

- Move all fingerprint related to logic in on central class in
SystemUI that knows all the state of the UI so there is exactly ONE
place in which we decide what to do when we acquire a fingerprint.
- When pulsing and we get a valid finger, we fade the contents of the
Keyguard out and fade the scrim out almost the same way as we would do
in a normal wake-and-unlock sequence.
- Hide shadows while dozing, so we don't see the artifacts when we fade
the dozed Keyguard out.

Bug: 23225107
Change-Id: I82f78e61f2530cf7d507ade80f6f0a340c082567