add triggering of custom actions by turning knobs

[Markse]

The Komplete Kontrol A series does not have the track select buttons and therefore cannot execute custom actions.
This change adds the triggering of a custom actions by turning the knobs.

Note: this also removes setting the volume in extended mode to avoid unintended volume changes. I assume this behavior was just a placeholder.

[terminar]

@brummbrum should we add a boolean (has_display) for the smaller devices without display/display buttons?
This patch is a good idea but I am not happy with the situation that it will change the workflow for all devices.
We can check for has_display=false and then, apply some logic as provided here.

[brummbrum]

in the current form this cannot be merged as it deteriorates the experience on the S keyboards with display. Obviously this could be improved by some additional logic like proposed by @terminar. While at it one could also improve the protocol details between these different device types (see my comments in niMidi.cpp (393ff) ). Right now it is forced to use protocol version 2, version 1 and 3 may be better suited for M and A series. But to be honest I have no time or desire to find this out myself....

[terminar]

I will take a look at it the next days.