Support of MaschineMk1 MIDI ports

[quasart]

Hello,

Here are developments I needed to access MIDI ports of my MaschineMk1.

• Messages sent to MIDI OUT port are now enqueued (otherwise I had a deadlock when sending midi from controller callbacks)
• MIDI IN port decoding (forwarded to virtual port)
• MIDI OUT port can also be populated throw a virtual port.

Any comment welcome

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This change is