Status bar brightness control improvements

- Prevent brightness changes after notifications panel has been opened.
- Don't adjust brightness for swipes <45° from vertical.
- Stop using a VelocityTracker since we weren't actually giving it any
  events to track.

Change-Id: Ie28c5c186b692e3f308bba4a1ee02faeb0982ac1
Merge "Status bar brightness control improvements" into cm-10.2