Ignore fader touch when learning and filtering source

[helgoboss]

At the moment, fader touch events make the "MIDI learn" experience a bit less great. The first event that occurs when using a fader is the "touch" event. In most cases, one wants to learn the fader move, not the fader touch. It would be better to ignore such events.

The question is: How to detect "Fader touch"? Since ReaLearn is controller-agnostic, it's better not to interpret certain MIDI messages as touch events. I think it would be best if the controller preset says which event is a touch event. We could introduce a flag "Is touch event" for virtual targets. Or even better: We could generalize it and name it "Learnable". There could be more events of this kind which are not suited for learning, e.g. controls with very sensitive aftertouch.

Plan:

• Add learnable flag to virtual targets. Should be true by default and for existing presets.
• Ignore virtual events with learnable == false when using "Learn source" (both the local "Learn source" and the global one!). Selecting such a source can be done manually instead.
• Also ignore such virtual events when doing source filtering. Searching such a source can be done manually instead.
• Important: Don't ignore it for processing! Of course, touch events matter. They are important for automation mode "Touch".