moved volume slider to bottom

The default positon of the volume slider is awkward when playing video, it will
often be located right over an actor's face during a standard close up.
A simple fix is to move the volume slider to the bottom part of the screen.
More information here: http://code.google.com/p/android/issues/detail?id=51233

Change-Id: Ib9eba45d9c95ea7919d4b9e4eb6cc739ae664a27
Signed-off-by: Hanno Zulla <hanno.zulla@epublica.de>