Feature Request: Allow GCState to be configured for controls

[ahall41]

This is primarily in conjunction with #1657, where it isn't possible to set GCState for a coupler manual coupler (so my real keyboard can default to at least one manual), but occasionally you may want this for something else. Perhaps add an override for GCState in the Midi configuration dialog?

[ahall41]

I'm now not sure this is absolutely necessary. Having just thought about it, an experiment shows me it is possible to trigger a preset with the GC Midi event, and GC is actioned first :-).