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

quantum/keymap_common.h

@@ -195,6 +195,7 @@ extern const uint16_t fn_actions[];
 
 
 
+
 // MAGIC keycodes
 #define MAGIC_SWAP_CONTROL_CAPSLOCK      0x5002
 #define MAGIC_UNSWAP_CONTROL_CAPSLOCK    0x5003
@@ -232,6 +233,10 @@ extern const uint16_t fn_actions[];
 #define MUV_IN 0x5024
 #define MUV_DE 0x5025
 
+// Midi mode on/off
+#define MI_ON  0x5026
+#define MI_OFF 0x5027
+
 // GOTO layer - 16 layers max
 // when:
 // ON_PRESS    = 1