cosmetic changes, removed the note attached to the onMidi function
various changes to faciliate parameter feedback to the bcf2000

- added an enable/disable output flag
- added an io_instance variable (not fully implemented)
- removed the body of the BCF.BCF2000Controller.prototype.flush function
- added BCF.BCF2000Controller.prototype.send_midi function
- added the output callback bodies for all the parameters
- used an array to index the tracks instead of a static variable (gets around closure issue)
- set controller.param in the BCF.build_control_layout function
- changed how the user buttons are generated slightly