cmake: add missing main.cpp

.../RobotAPI/applications/ForceTorqueObserver/CMakeLists.txt

source/RobotAPI/applications/ForceTorqueObserver/main.cpp

source/RobotAPI/applications/MotionControl/CMakeLists.txt

source/RobotAPI/applications/MotionControl/main.cpp

...ce/RobotAPI/applications/MotionControlTest/CMakeLists.txt

source/RobotAPI/applications/MotionControlTest/main.cpp

source/RobotAPI/applications/TCPControlUnit/CMakeLists.txt

source/RobotAPI/applications/TCPControlUnit/main.cpp