Patcher Instance MIDI control: note held if keyboard key is down and tab is switched

[benbrackenc74]

To repro:

1. export a patch that has MIDI control, fe rnbo.remote help patch's remote_example
2. in graph editor on the pi, add patcher instance of the export
3. in graph editor on pi, hook up audio output
4. in patcher instance control->MIDI, hold down a note on computer keyboard
5. while note is held down, change tabs back to Parameters
6. release keyboard key - note still held down

Could have a flush when switching tabs/views, and/or have an all notes off panic/reset option for MIDI

Probably another ticket, but it would be nice if there was a virtual MIDI piano “device” in the graph editor that you could connect to any midiin, instead of it being patcher instance-specific.

[benbrackenc74]

related to issue #45 (MIDI panic button)