Post-review Keyguard cleanup.

- remove userActivity() from KeyguardService interface and call it
on PowerManager directly
- Split IKeyguardResult into two parts: IKeyguardShowCallback and
IKeyguardExitCallback.
- Misc other changes from the review.

Change-Id: I3f679cfa5d3f8bc742f2b2259ac354045e89a87b
12 files changed