Optionally map part buttons to one of the mixers

[christeck]

During the programming process, a quick possibility to switch oscillators on and off would be appreciated (the Korg Z1 provides front panel buttons for Osc1, 2, sub, and noise). Since I often work with one part only, the four part buttons are often left unused. Remappign the part buttons from the VCAs to mixer1, 2, 3, or 4 came to my mind .