Only duplicate notifications when no media is playing

Map the NOTIFICATION stream type to a new strategy,
 named STRATEGY_NOTIFICATION_RESPECTFUL, which differs
 from STRATEGY_NOTIFICATION in that, when media is
 playing, the notifications will use the same output
 as the MEDIA strategy. This will results in the
 notifications not being duplicated on the speaker
 when a headset is in use for media playback.

Change-Id: I032be0e2d383c69b5b6c912d7174753f5572c4b4
3 files changed