Add group exclusivity option

[helgoboss]

Automatically send control value zero to all other mappings in same group when controlling one mapping with a value > zero.

[helgoboss]

Should be a tuning option, independent of the target.

[daniboyle]

This would be perfect for mapping opposite values of MIDI passing effects on different instrument tracks.

https://forum.cockos.com/showpost.php?p=2440730&postcount=1270

[helgoboss]

Should be more general:

• It should send the inverse value with respect to the target range.
• E.g. if target min is 50% and max is 90% and an incoming control message sets the target to 80%, the targets of the other groups should be set to 60%.
• This makes it usable for range controls (non-buttons) as well.