GCS_MAVLink: add support for send_mission_item_reached

libraries/GCS_MAVLink/GCS.h

@@ -141,6 +141,7 @@ public:
     void send_autopilot_version(void) const;
     void send_local_position(const AP_AHRS &ahrs) const;
     void send_vibration(const AP_InertialSensor &ins) const;
+    void send_mission_item_reached(uint16_t seq) const;
 
     // return a bitmap of active channels. Used by libraries to loop
     // over active channels to send to all active channels    

libraries/GCS_MAVLink/GCS_Common.cpp

@@ -1336,3 +1336,11 @@ void GCS_MAVLINK::send_vibration(const AP_InertialSensor &ins) const
         ins.get_accel_clip_count(2));
 #endif
 }
+
+/*
+ * send notification that a mission command has been completed
+ */
+void GCS_MAVLINK::send_mission_item_reached(uint16_t seq) const
+{
+    mavlink_msg_mission_item_reached_send(chan, seq);
+}