Feature/urdf parser py

From [this issue thread in robot_model_py](https://github.com/laas/robot_model_py/issues/4#issuecomment-20947614) - These changes incorporate urdf_parser_py, including newer features in the 'master' branch (currently supporting groovy / hyrdo).

I have run the unittests in calibration_estimation (the only package that seems to have depended on urdf_parser) and verified that there are no differences in running with these changes: [unittest comparison](https://github.com/eacousineau/calibration/blob/c619998fb3e5ae20a4c193884b949e69c4518a13/calibration_estimation/urdf_parser_py-unittests.txt)