Implement instrument switcher

[emilis-wix]

Ableton merges MIDI mapped CC's from all MIDI ports, but differentiates them by MIDI channel.

• Assign MIDI channels to instruments. Send instrument change CC (0) on the appropriate channels.

Maybe we should also update the Ableton project to use one MIDI port and different channels for the instrument tracks.

Suggested channels:

1. reserved for Ableton ←→ MIDI magic control
2. bass
3. drums
4. guitar
5. keys