Cleans up a lot of code, removes handles for now.
These are present in the netstandard branch (the rules aren't working there - probably using the wrong configuration).
Also adds variant to settings
Fixes https://github.com/ppy/osu/issues/1625 .
Fixes #1911. This follows what osu!stable does, which is rather unfortunate, since it just plays _every_ sound for the note :|.