Implement basic root mode

[mickmister]

The idea of root mode is to be able to press a single note, and have jam tools play a predefined chord shape on midi devices that are configured to receive "noteon" midi events. Ideally we can support commanding different chord shapes simultaneously to different midi devices, but for this initial effort it will be one chord shape assigned to a given midi root note.

Exactly how the chord shapes are initially configured into the program is TBD. That is really the "data entry" task here #40. Hardcoding the chord shapes in some config file is file for now. One chord family can live in one JSON file for now, or something similar to that. The requirements are essentially undefined for this atm.

I would like to couple this issue with #11, which will allow the tonal person to easily command the chords to play and be silent when desired.