Trigger multiple instruments by a single MIDI NOTEON

[theGreatWhiteShark]

Currently, when "Use output note as input note" is checked in the Preferences, only the first instrument matching the incoming MIDI note key will be played back.

While I wouldn't consider this a bug or having multiple instruments with the same note a feature, this behavior is still a little bit unexpected when toying with or developing drumkits. In edge-cases it will annoy people (see #599).

I would suggest we trigger notes for all instruments matching the incoming note.