Support for Audio-Only files

[jduehring]

With this PR: https://github.com/opencast/opencast/pull/5856/files Opencast will be able to process and play audio-only files. I added some changes to the OC PaellaPlayer in order to make this work.

There is the need to do equivalent(?) changes to the PaellaPlayer used in Tobira in order to play them in Tobira as well.

To test this you would need to apply the mentioned PR to an Opencast system, upload an audio-only file using the standard workflows and try to play it through Tobira.
Alternatively you could just use the updated encoding profile and workflows from the PR. This should be enough to upload and process the audio-only, but not play in in Opencast directly. But for testing the Tobira playback it might be sufficient.