PowerManagerService: Implement setButtonBrightnessOverrideFromWindowManager method

Differs from Android 4.1 (and earlier) implementation in that the
overridden button light still turns off after BUTTON_ON_DURATION instead of
staying on until screen off.  However, button lights are annoying, and
really the purpose of this is to allow apps (e.g., Screen Filter) to
_disable_ the button lights altogether.
Fix Quiet Hours not muting notification sounds

4.2.2 touched the NotificationManager service, and some logic went missing in the merge it seems.
This should take care of it.

Change-Id: Ib3b88c83d2936871fbe25f1acbd10fd60c577944