Pinocchio IK with MJCF #201

It should be possible to use the mjcf as a base for the pinoccio ik. Implementation has already been started to this branch. However, there are a few issues that come up while integrating it:

• you need use the robot mjcf file and not the scene file. Includes seem to not work in the pinocchio mjcf parser
• xml options "compiler", "option", "default" and "asset" need to be inside the xml file given to pinocchio
• the mjcf has to have all definition on the top as the pinocchio compiler only does a single run
• it seems as if the gravcomp tags are not supported, so we might need a way to remove them before feeding into pinocchio

Definition of done

• cartesian example is working with mjcf xml file
• define a way to get the robot mjcf file (parsing out of the scene file or directly specifying it)
• remove the gravcomp tags automatically in a temp location before reading the file in
• test that the cartesian example is also working for other robots (UR5 and so101), they are implemented in UR5 Integration and Pinocchio MJCF IK #197
• a small test that tests inverse and forward kinematic calculation of pinocchio and robotics library