Added instantiation of objects for subscription to fcu-related ROS topics
Added ROS callback functions prototype for asctec_mav_framework-related topics
Sorted out call to getParam() to fetch double type
Implemented asctec_hl_comm/imu_custom callback and modified scale of variometer
Implemented sensor_msgs/NavSatFix callback
Implemented asctec_hl_comm/mav_status callback function (review needed)