CREO2URDF – Modify how the joints are defined in the upperbody assembly

[Nicogene]

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We should modify the assembly we used for MVP-2.5 (see #33) defining the joints (fixed and revolute) in "all" possible ways.

This will be useful for testing how creo2urdf is able to generalize.

We should talk w/ @fiorisi for understanding which are the possible ways for defining joints

cc @pattacini @mfussi66