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

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

PS: make "TRDS default" summary value a resource so
        it can be translated.

Change-Id: Ic788b4ccf1826075a600e53bc6a7c3c8bda50685
Update Slimrecents background color && transparency [1/2]

Add missing part... Taken from here:
https://github.com/SlimRoms/packages_apps_Settings/commit/f7893f1091b2fba0b84b67ea0b2374e843db7624

Change-Id: Icfa6abc98a2fe106c58af30bfba7098db1812960