add ruby extension extension lookup to also support OSX

Signed-off-by: Ruben Smits <ruben.smits@mech.kuleuven.be>
remove the use of hosted gems

Signed-off-by: Ruben Smits <ruben.smits@mech.kuleuven.be>
catkin: add CMakeLists.txt that installs utilrb and add package.xml to make it buildable with catkin

Signed-off-by: Ruben Smits <ruben.smits@mech.kuleuven.be>