Option to use volume keys to control media volume anytime [1/2]

The volume keys control the Media volume rather than the Ringer
hence removing the issue of accidentaly changing the Ringer volume.

Credits: Pawitp

Change-Id: I789e05bdb0bb7c968f71e4e10f4a759b3dbd0b59
Merge commit 'refs/changes/55/855/1' of https://gerrit.slimroms.net/SlimRoms/frameworks_base into vaosp