CK main loop: filter all real-time messages

[narcode]

• Clock (248)
• Reserved (249, 253)
• Start (250)
• Continue (251)
• Stop (252)
• Active Sense (254)
• Reset (255)

[narcode]

This has to be investigated more because it affects the way th deltatime is sent from manufacturer to manufacturer. In short, needs attention and a flexible solution.

Casio case: use low-res MIDI