move SafetyEnvironmentCreator to library and add header file

CMakeLists.txt

src/SafetyAwarePlanner.cpp

src/SafetyEnvironmentCreator.cpp

src/SafetyZones/GazeboZoneSpawner.cpp

src/SafetyZones/GazeboZoneSpawner.h

src/SafetyZones/SafetyEnvironmentCreator.cpp

src/SafetyZones/SafetyEnvironmentCreator.h

src/robot_control_node.cpp