Settings: Forward port Volume button music controls

FW side already exists.

Original author: Danesh Mondegarian (devatwork)

Change-Id: I174fa5ec72e36e29d7c8d139213905f3327f6aae

Conflicts:

	res/values/strings.xml
	res/xml/sound_settings.xml
	src/com/android/settings/SoundSettings.java