Add stepmania *.sm compatibility

[alejandro-alzate]

Mentioning #45 it'll be cool if we could shove accurate charts to the game
Then in game BPM-based chart shouldn't be needed this badly.
And mappers just would use Arrow-Vortex and alike

[alejandro-alzate]

Here's a demo video, of a chart that i made on AV (the speed changes is so yt doesn't get mad at me): https://www.youtube.com/watch?v=OSW5U-LQcNU