Track listens through HLS segment serving

[simonv3]

When we serve audio through HLS streams we can intercept each segment fetch and check for the user's credits as well as if it's a free play or not. This way we don't have to rely on the front-end to implement registering a song as played as well storing a trimmed version of each song, we just cut it off. That will drastically reduce the number of endpoints we have to maintain for song playing, as well as front-end code to implement it.

To do this we first need to convert all of our existing audio to HLS format.