Increase available volume levels

Increase media volume levels from 15 to 30 to have more precise
volume control instead of having only 15 levels from 0-100%

For example, when listening to music it is often the case that one
volume level is too quiet and the next one higher is too loud (especially with Headsets).

Signed-off-by: Michael Bestas <mikeioannina@gmail.com>

Change-Id: I7a8750c901967ce3c818fb9c33b082af6b86b8d6

Conflicts:
	media/java/android/media/AudioManager.java