Generating MIDI CC for all signals but gyro.

- Added min and max properties to MIDIGenerator.
- Configuring appropriate min/max for generators.
- Added combo boxes for y,z,ax,ay,az.
- Renamed -xMidiCCDidChange: to -midiCCDidChange, extended it to pass
  CC selection to all generators.

Signed-off-by: Chris Reed <flit@me.com>