ID tune versions by key

[davetapley]

Currently tune versions are ID by their index in the array returned by match_notes.
These IDs aren't canonical, and can prevent a user viewing a transpose unless it's a complete (or the current 'best') match.

[davetapley]

@Annie123 okay this is live, you can now add any key to the end of a /versions URL and it'll give you the transpose, e.g;

http://dingr.herokuapp.com/tunes/9/versions/G7

Available players will get their normal color notes, and any unavailable will just be white.