updates midi functionality (#331)

* implements leader key for planck experimental

* allows override of leader timeout

* adds ability to use the leader key in seq

* fixes leader keycode

* adds chording prototype

* fixes keycode detection

* moves music mode to quantum.c

* disables chording by default

* adds music sequencer functionality

* implements audio/music functions in quantum.c

* splits up process_action to allow independent processing of actions

* moves midi stuff to quantum.c

* adds additional scales for midi

tmk_core/protocol/lufa/lufa.c

@@ -883,7 +883,7 @@ int main(void)
     midi_register_cc_callback(&midi_device, cc_callback);
     midi_register_sysex_callback(&midi_device, sysex_callback);
 
-    init_notes();
+    // init_notes();
     // midi_send_cc(&midi_device, 0, 1, 2);
     // midi_send_cc(&midi_device, 15, 1, 0);
     // midi_send_noteon(&midi_device, 0, 64, 127);