added merge to reserve only midi notes and cc's on the channels defin…

[evgenyslab]

Modified the way build_midi_map executes so that it only reserves the notes and cc's on specific channels. As far as I could understand, in the original implementation, build_midi_map reserved the notes and cc's from the built callbacks on all channels; this made it not possible to send actual notes with a controller to the track, i.e. if I wanted a keyboard controller to use half of the keys set to channel 1 to control Live, while the other half on channel 2 to play notes; this was not possible unless I removed the corresponding notes from settings.py.

Hope this change makes sense, could also make it variable based :)