Re-implement chords to support better inversion and root preservation

Chords are currently dumb objects that do not remember the intended root between inversions. This can make for odd results on repeated inversions.

Chords should probably be re-implemented to preserve the original root note, so that inversions or note modifications can be better tracked and displayed. For example, Chords where notes are omitted or added should be easy to introspect such details. Currently, all are thrown into one vector.