navigator geofence: switch to new dataman data structure, support multiple polygons

This also removes the 'navigator fence <lon> <lat>' command to simplify
code (I don't think there's still use for that anymore). However the
file loading is still supported.

If goefence.txt does not exist, navigator will not clear the geofence
anymore on startup.

src/modules/navigator/CMakeLists.txt

@@ -30,6 +30,9 @@
 # POSSIBILITY OF SUCH DAMAGE.
 #
 ############################################################################
+
+include_directories(${PX4_SOURCE_DIR}/mavlink/include/mavlink)
+
 px4_add_module(
 	MODULE modules__navigator
 	MAIN navigator