Norns: Expand MIDI-learn to all MIDI channels

[okyeron]

Looking at the menu.lua code for midi-learn it looks like it only works with CC messages on channel 1.

We could expand this to look at all the CC channels by

if data[1] > 176 and data[1] < 192 then -- all cc channels

but then we would need to store the channel number in m.params.map somewhere.

How best to do that?

[tehn]

midi learn overhaul is forthcoming in the new parameter system/menu/interface.

i'll be sure that channel is mappable.

[okyeron]

Let me know if I can help :)

[okyeron]

Additional feature request:

Make Levels controls mappable to midi CCs (system volume, input, mon, engine, tape, cut)

[rbxbx]

as @okyeron suggests, I basically always want a (tactile) gain control for the norns. Relying on being attached to a mixer (that you have control over) is kind of a bummer, especially for lightweight sessions.

[okyeron]

Closing as this appears to be done with #960