This commit introduces the new video_widget.

- The video_renderer has been reworked to take a Clutter Texture as
  parameter and render the video inside.
- The video_callback has been rewritten and now only handles the dbus
  callback.
- The new class video_widget handles all the stuff related to the video
  window, the clutter scene is a part of it.
- The dbus callbacks started_decoding_video_cb and
  stopped_decoding_video_cb are passed the SFLclient as a parameter
- A workaround has been added by Tristan Matthews to handle a bug in clutter 1.16
- Fix a bug where the remote camera doesn't fill all the widget space

Refs #46425
Refs #47873

Change-Id: If60dae9acedb1835cc2885f5f29fd7ea5be0757e