Implement stacked, controllable chords for carrier

[cwilso]

via Chris Rogers:

I was thinking that if you had 3 stacked oscillators then you could play musical "triads" and assign the keyboard keys to change chords and modulate to different keys. You could have a simple JSON structure with the triad semitone (or "cents") values... I think this would add a lot since you could play chord progressions rather simply this way. Obviously MIDI will be way better, but in the meantime...