TEST
source code: https://github.com/arturmiller/minimal_example/blob/master/src/py_contact_sensor.cpp
Gazebo ContactSensor: https://bitbucket.org/osrf/gazebo/src/bd1cdea8fa3d71d6afcdaa83c9b01891d5f72e71/gazebo/sensors/ContactSensor.hh?at=default&fileviewer=file-view-default
CMakeLists.txt: https://github.com/arturmiller/minimal_example/blob/master/CMakeLists.txt
stack-trace: https://github.com/arturmiller/minimal_example/blob/master/error.txt