Allow publishing of non-audio and non-video artifacts

[Kunsi]

... like subtitles (.srt)

[derpeter]

So far we get the files source URI form the tracker. The tracker usually gets it from a schedule.xml. If we want more file types we should have a clear idea where to get the URLs from. e.g.
a) new tracker propertie
b) gues it from the video URL
c) complete new source of information

Also in the past SRT usualy was not present when the video files where released. We need a way to trigger the process later on. Maybe a new ticket type / profile in the tracker could be used. @a-tze thoughts?

[Kunsi]

My current idea was:

• SRT files get somehow™ onto the releasing vm
• voctopublish handles the upload

If we support this in the recorder script, we might need another Property like Fahrplan.SubtitleDownloadURL, which then could also have an optional element in the schedule.xml spec. Might need another recording ticket in the tracker though, which might be a bit out of scope here. Alternatively we could download it together with the video file in one recording step.

For now, i'm happy with "upload it to releasing and just upload to youtube" for now. voctopublish just needs to understand that, which is why this ticket exists (and why i'm working on that right now)