quiet hours: add back the option to disable system sounds (1/2)

Change-Id: Ie494c441c3e0e48a5394fce3f5e0ef671c3d085f
Signed-off-by: Dan Trifan <jimsth@gmail.com>

Conflicts:
	core/java/android/provider/Settings.java
	core/java/android/view/VolumePanel.java