MIDI input does not respect channel

[theGreatWhiteShark]

Using the option 'Use output note as input note' in Preferences > MIDI System incoming MIDI note events can be mapped to the instruments via their settings in Instrument Editor > MIDI Output. At least partially.

Currently, only note key but not channel number is used. MIDI notes are played back for the channel(s) set in Preferences > MIDI system regardless of the settings in the Instrument Editor. That's inconsistent and could be a nuisance when Hydrogen is used in a larger setup.

When implemented, Preferences > MIDI system has to be slightly changed. Channel dropdown should be hidden or disabled once 'Use output ...' is checked.

Related to #1626