Volume Rocker: Hardcode music track seek option (1/2).

* The feature is enabled by default but not configurable.

Signed-off-by: Carlo Savignano <stevewatersy@gmail.com>

PS2:

* Remove unneeded variables.

Signed-off-by: Carlo Savignano <stevewatersy@gmail.com>

Change-Id: I0c72dd00f8a161255a59330862fa69c66735a3e4
MediaFocusControl: Do not grant audio focus if notification stream is 0

Previously audio focus would be granted regardless of notification volume, meaning
that if notifications are muted the media stream would still be dimished for focus.
By checking if STREAM_NOTIFICATION is 0 and if a notification stream is
requesting focus, this no longer an issue.

PS1: Initial implement
PS2: Better implement in MediaFocusControl
PS3: Whitespace

Change-Id: Ie10a64e58ce77174a3bbdeaa936646d40c24404f
Signed-off-by: Evan Anderson <evan1124@gmail.com>