Fix VAAPI playback when OpenGL2 painter is used

For some reasons, VAAPI doesn't work with the OpenGL2 painter, instead you get a black window.
As I do not have at present the skills to identify the issue, implement a work around:
- If we are using the OpenGL1 painter, re-use the main UI painter
- If not, create a new OpenGL1 render context and use it instead.

This also allows to use VAAPI with the Qt painter (the requirement that OpenGL be present is still present) and not just error-out
Allow PiP when using a VAAPI playback profile

Two VAAPI streams at once still doesn't work (causes video corruption), but still should be able to use PiP regardless.
Fix GetChannelInfo when sourceid is specified.
Merge remote-tracking branch 'upstream/master'