Make it possible to send virtual control messages to other ReaLearn instance

[helgoboss]

Just an idea for now, not sure if it will ever happen.

Use cases

I have the following use cases in mind

Multiple controllers doing the same

This is nice for live if one wants to take different controllers depending on the occasion - a minimum setup, a luxury setup, etc.

Instead of having to duplicate instances and modify them accordingly (which doubles maintenance), we could just map control elements of each controller to the same virtual control element ID.

Exposing multiple controllers as a virtual big one

Not too useful but we would get this for free.

Implementation

• Shouldn't be hard for the control direction.
• Feedback direction is more complex, so skip that for now.
• Making this a target would probably be the best option because then we can still use clean controller presets in the corresponding instances and do the "normalization" (mapping to dedicated virtual control elements) in the corresponding target.