* [loader] SDF support

Co-authored-by: Guilhem Saurel <guilhem.saurel@laas.fr>

* [bugfix] Included the velocity limits in the talos-legs model

And activate tests again

to avoid a dependency to https://github.com/stack-of-tasks/talos-data/
in many packages

and document their purpose

Which lead to find that __main__ was missing the variations of icub &
ur5

Gathering all expected available robots and parameters in one dict
indexed by names avoid the need to duplicate those informations.

when it was useless otherwise

With trivial factorizations,
to avoid code duplication and ease future robot addition.

While here:
- deprecate `loadTalosLegs()` for the factorized `loadTalos(legs=True)`
- use cleaner `os.path.join()` for file path manipulation instead of
  string concatenation

which is the standard way of using pinocchio, according to its examples
and unittests.