commander: take main_state out of vehicle_status

This state is only commander internal. Therefore it doesn't need to be
in vehicle_status. Instead it is now in the commander_state message.

msg/commander_state.msg

@@ -0,0 +1,31 @@
+# Main state, i.e. what user wants. Controlled by RC or from ground station via telemetry link.
+uint8 MAIN_STATE_MANUAL = 0
+uint8 MAIN_STATE_ALTCTL = 1
+uint8 MAIN_STATE_POSCTL = 2
+uint8 MAIN_STATE_AUTO_MISSION = 3
+uint8 MAIN_STATE_AUTO_LOITER = 4
+uint8 MAIN_STATE_AUTO_RTL = 5
+uint8 MAIN_STATE_ACRO = 6
+uint8 MAIN_STATE_OFFBOARD = 7
+uint8 MAIN_STATE_STAB = 8
+uint8 MAIN_STATE_RATTITUDE = 9
+uint8 MAIN_STATE_AUTO_TAKEOFF = 10
+uint8 MAIN_STATE_AUTO_LAND = 11
+uint8 MAIN_STATE_MAX = 12
+
+# If you change the order, add or remove arming_state_t states make sure to update the arrays
+# in state_machine_helper.cpp as well.
+uint8 ARMING_STATE_INIT = 0
+uint8 ARMING_STATE_STANDBY = 1
+uint8 ARMING_STATE_ARMED = 2
+uint8 ARMING_STATE_ARMED_ERROR = 3
+uint8 ARMING_STATE_STANDBY_ERROR = 4
+uint8 ARMING_STATE_REBOOT = 5
+uint8 ARMING_STATE_IN_AIR_RESTORE = 6
+uint8 ARMING_STATE_MAX = 7
+
+# state machine / state of vehicle.
+# Encodes the complete system state and is set by the commander app.
+uint64 timestamp # in microseconds since system start, is set whenever the writing thread stores new data
+
+uint8 main_state		    	# main state machine