Improved separation of ASM and enabled video playing.

Improved separation of ASM and enabled video playing.

Improvement of the separation of the audio session manager using the
compiling option ENABLE_TIZEN_AUDIO_SESSION_MANAGER. It solves a
bug on the mute status of the media elements (TZ:bug 3809).

Addition of the compiling option ENABLE_TIZEN_GSTREAMER_VIDEO_SET_SINK
that enforces to use the webkit sink. It allows to play video on
surfaces.

Activating option ENABLE_TIZEN_GSTREAMER_VIDEO_SET_SINK
for GStreamer 1.0 (surely to be changed in futur)