Optimize underwater music, add .ogg files

[joshlory]

The added aquatic 01-03 mp3 files are much larger than previous years. We'll also need the .ogg version for our sound player.

https://github.com/code-dot-org/craft/blob/5a8b2378b4bfb0e7d9d68de4b768ca947455e9df/src/assets/audio/ogg2mp3#L1-L2

The nether music from last year should also be optimized.

[joshlory]

These seem to be about the same bitrate, but the samples are much longer. Can we ask Neal for smaller "vignette" versions of the longer music, so we can start playing as soon as the first one is loaded?

This'll also add variety to the six underwater levels, because we can start at a different point in the track (different short clip) for each.