Option to use volume keys to control media volume anytime (1/2)

Some users don't adjust ringtone volume often (e.g. only use toggle to
switch between silent and non-silent) mode. Having an option to
use the volume keys to control media volume anytime allows media
volume to be controllled/muted before entering a game or other apps
with sound in an undesirable location.

Change-Id: I6dbd25d1a14bcf5b1bf0b0468b96f4b4f8efdb14
Performance Settings: Enable KSM by default for lowmem Devices (512Mb)

Change-Id: I7bb688f412a7156dae628b170ac4c919a36f3cb3