Added support for switching to AUTO mode in Autopilot.

When the application is started with the command parameter "plane", the
application uses the AzDroneControllerPlane class to control
initialisation. It doesn't arm or takeoff the drone. Instead, it waits
for the user to mode to AUTO (in Ardupilot, Mission in MAVSDK) with the
RC controller. When AUTO mode has been detected, the application will
start a normal mission handling.

src/az_drone_controller_plane.h

@@ -0,0 +1,15 @@
+#pragma once
+
+#include "az_drone_controller.h"
+#include <QObject>
+
+class AzDroneControllerPlane : public AzDroneController
+{
+    Q_OBJECT
+public:
+    explicit AzDroneControllerPlane(AzMission &mission, QObject *parent = nullptr);
+
+protected:
+    void droneStateMachineSlot(void) override;
+    bool stateWaitingMissionMode(void);
+};