FS-7513: Example code to use the core video thread with a custom callback

FS-7513: Example code to use the core video thread with a custom callback

It by default remains the default behaviour

However, you can setup a relationship between members to let the
member choose to see anyone else but the floor, e.g.:

  conference 3000 relate 1 2 sendvideo

In the above command member 2 will see member 1's video regardless
member 1 has video floor or not