Improve auto-brightness handling
- Add a setting to control the auto-brightness algorithm responsitivity
- Make the algorithm react much faster when the ambient brightness
  increases quickly, e.g. when receiving a call in bright sunlight.

Conflicts:
	services/java/com/android/server/power/PowerManagerService.java

Change-Id: If9a6790c95ce8c2afdb40b21ecd5cafd443ce5a3