Add support for per service list of supported audio codecs

Currently only handles the vanilla OBS case of two possible codecs, i.e.
it won't list multiple listed supported codecs as alternatives in the
warning message; also doesn't verify that the listed codecs are actually
available in OBS

Other than that it supports multiple "supported audio codec" entries
in services.xconfig per service, in case anyone wants to white list
both MP3 and AAC for their service:

```
recommended : {
 "supported audio codec" : "MP3"
 "supported audio codec" : "AAC"
}
```
Add AAC as supported audio codec for hitbox.tv (i.e. black list MP3)

Using MP3 breaks sound in VODs according to @Gol-D-Ace