+ Reduce the complexity of, and refactor the video management code.
+ Replace the directrenderer pipeline with one that permits clients
  to map and provide a custom video buffer.

Note: this removes the "useAVFrame" path for now.

Gitlab: #500
Also jami-client-qt#536

Change-Id: Ia326c452c7887086acc75e8eb52fa24b7f4cf25b