Land drone safely

- improved landing
- navigate to the return point defined in JSON file
- land drone safely without timeouts

Issue: https://denyspopov.atlassian.net/browse/AZ-24
Type: New Feature

src/az_drone_controller.h

@@ -64,9 +64,6 @@ private slots:
     // Called at the end of the mission. Lands and disarms the drone.
     void missionFinishedSlot(void);
 
-    // Disarms the drone and exits the application. TODO!! Discuss quitting the application.
-    void disarmDroneSlot(void);
-
     // Gets Telemetry::Health information in prearming.
     void newHealthInfoSlot(Telemetry::Health health);