better handling of wrl conversion.  resolves #286

the only interesting change is to the logic in RigidBodyMesh.m

removes .wrl files from atlas directory since they are now made (correctly) from the stl files on the first call when they are needed.  
there are other wrl files kicking around in the repo, but they are not generated from stl so I will have to wait until i bring more converters online (robustly).