AP_BattMonitor: fixed example build

libraries/AP_BattMonitor/examples/AP_BattMonitor_test/AP_BattMonitor_test.pde

@@ -14,6 +14,20 @@
 #include <AP_HAL_PX4.h>
 #include <AP_HAL_Empty.h>
 #include <AP_BattMonitor.h>
+#include <GCS_MAVLink.h>
+#include <DataFlash.h>
+#include <AP_GPS.h>
+#include <AP_InertialSensor.h>
+#include <AP_Baro.h>
+#include <Filter.h>
+#include <AP_AHRS.h>
+#include <AP_Compass.h>
+#include <AP_Declination.h>
+#include <AP_Airspeed.h>
+#include <AP_Vehicle.h>
+#include <AP_NavEKF.h>
+#include <AP_Notify.h>
+#include <AP_Mission.h>
 
 const AP_HAL::HAL& hal = AP_HAL_BOARD_DRIVER;