Fix Master test; adding check that config was sent to slave
tests/source_file: Speedups via chunk_duration
Transcoding: Use error domain

* TranscodingSource: Wrap functionality in a domain to catch any funky
  things that happen if ffmpeg dies or we're shutting down. Call disconnect
  if we get a domain error
* Update Transcoding tests
Transcoding: Spawn a new transcoder if one disconnects

* StreamGroup: Add listener for the transcoder disconnect. Start a new
  transcoder if one disconnects.
* TranscoderSource: Stop our debounce listener when disconnecting