* Use Instrument::get_midi_out_note for MIDI export
 * Assign sequential midi_out_notes to instruments instead of middle C
 * Modify MIDI note numbers in drumkits to match GM spec
 * Initialize p_midiDriverOut to CoreMidi
Merge branch 'midi-fixes' of git://github.com/elpescado/hydrogen into elpescado-midi-fixes

Conflicts:
	src/core/src/hydrogen.cpp
Merge branch 'elpescado-midi-fixes'. Leave out CoreMidiDriver fix since
midi out is not implemented yet.