Users may upload MP3 files.

This crams audio files into the Video model. I tried creating a class that inherited from Video and ignored things like frame information, but something deep down was trying to access these properties and was causing errors.

In the meantime, when uploading audio files, the document's type uses "humaudio." I figure we can go through and clean up our data when we have something that works a little more nicely.

The tests use public domain audio files.