copySessionDescription adds a button to all examples that copies the
local Session Description. This makes it easier for users to copy the
values.
Resolves#2092
Use offerer PayloadType when generating answer. Before we would use the
hardcoded values, this is invalid behavior and would cause browsers to
just ignore our video when publishing.
Will have new dedicated SFU example when re-negotation
is complete. Keep this broadcast example for users who
want fan-out example and not everything needed for multi-track
re-negotations.
Relates to #207
