content: add some padding to class
documentation: add video sink
ClutterGstFrame: copy pipeline instead of taking ref

This is important if a video frame is painted in multiple actors with
different opacities.
plugin: add debug category for video sink
introspection: use same pkg as compile flags
auto-video-sink: rename to avoid GType name conflict with 2.0 version
utils: remove deprecation warning
video-sink: add overlay support
contents: add overlay support
sink: position RGBA GL upload as first cap
VAAPI DEBUG