cogl-gst: video-sink: use intended GStreamer API for data/stride/etc...

Based on a patch for ClutterGst from Matthieu Bouron <matthieu.bouron@collabora.com>
cogl-gst: video-sink: rework color conversion to care about colorimetry
cogl-gst: video-sink: add video balance support
cogl: winsys: glx: fix valgrind complaint
cogl-gst: video-sink: rework caps exposure
cogl-gst: video-sink: add shutdown method on renderers
cogl-gst: video-sink: add gl upload support
wip: video-sink: add navigation support