Settings: Volume panel background color && transparency [1/2]

Allow user to specify background color and transparency level
    for volume panel.

Conflicts:
	res/values-de/slim_strings.xml
	res/values-fr/slim_strings.xml
	res/values-it/slim_strings.xml
	res/values/gummy_strings.xml
	res/xml/sound_settings.xml
	src/com/android/settings/SoundSettings.java
	src/com/android/settings/accessibility/AccessibilitySettings.java

Change-Id: Ic788b4ccf1826075a600e53bc6a7c3c8bda50685