OutputEssence: raise exception in setup instead of return false

OutputVideo and OutputAudio: raise runtime_error if "could not allocate"
or "could not open" video / audio codec.
OutputAudio: remove checks of profile

The job is done by FFMPEG during setup!
Audio profile: remove channel layout requirement

Fix: the channel layout is not required by FFMPEG when open audio codec context. So an audio profile has not to set this value.