The previous se3 namespace is now deprecated but can still be used

[C++][unittest] Added unittest geom.cpp . It tests that we obtain the same results between Pinocchio and hpp-model-urdf for joints and geometry objects positions ; for collisions and distances between two geometry objects

  * One Definition Rule was still not enforced.
  * Declare function in header sample-model.hpp, implement them in
    sample-models.cpp
  * Add sample-models symbols to libpinocchio.

  * se3::Model::getBodyId was used to retrieve joint id in parsers.
  * Implement new methods to retrieve joint ids.
  * Fix body methods.