remoteid: implement System as sent from GCS

This will send the System message if it is already being sent by a ground
station. Otherwise, it will assemble the message itself using the
takeoff/home location.

msg/CMakeLists.txt

@@ -155,6 +155,7 @@ set(msg_files
 	OpenDroneIdArmStatus.msg
 	OpenDroneIdOperatorId.msg
 	OpenDroneIdSelfId.msg
+	OpenDroneIdSystem.msg
 	OrbitStatus.msg
 	OrbTest.msg
 	OrbTestLarge.msg

msg/OpenDroneIdSystem.msg

@@ -0,0 +1,13 @@
+uint64 timestamp
+uint8[20] id_or_mac
+uint8 operator_location_type
+uint8 classification_type
+int32 operator_latitude
+int32 operator_longitude
+uint16 area_count
+uint16 area_radius
+float32 area_ceiling
+float32 area_floor
+uint8 category_eu
+uint8 class_eu
+float32 operator_altitude_geo