Fix issue #35, arpeggiator notes in wrong order
Set velocity from internal keyboard to mid range, i.e. MIDI 64

* Applies both to notes played on the keyboard and from the arpeggiator.
* We use 32768U, as UINT16_MAX>>9 yields 63 instead of 64, and there's
  no other nice symbolic way to say 'half of UINT16_MAX+1'.
Added MIDI reception of hold pedal

* Shift up all stepped parameters past CC 64 one step.
* Just a stub for the actual hold function for now.
Implemented hold pedal in assigner