[WIP] Use MIDI controllers as analog controls

[sastraxi]

Allow configuring named ALSA MIDI ports as ; capture and forward MIDI messages to MOD / use as blend mode controllers.

Hasn't been tested a lot, but worked when I tried with blend mode. We need a custom version of MOD-UI to make this work, otherwise it will get duplicate MIDI messages (and always choose the hardware one first): TreeFallSound/mod-ui#3

The justification behind "capturing" it:

• we need it for blend mode to work, as MOD has no concept of the feature
• users can swap out their MIDI devices without re-binding every pedalboard