Useful when one does not known which robot will be loaded.

Call simply model.check(data)

[C++][unittest] Fix computations in jointcomposite::calc() + reworked unittest (comparison of R3xSO3 (either two joints with no inertia between them or Jointcomposite))

[C++] Removed default parameters for bounds when adding joint and created an overloaded method instead. Switched the order for addJoint method (put the default valued argument at last position)

[C++] Make JointComposite part of the JointVariant. Reoganized some include to avoid circular dependencies

[C++][unittest] Added neutralConfiguration vector in Model, and fill it when adding joints + test on neutralConfiguration

Renamed JointXXAccessor to JointXX + renamed traits<D>::JointData to traits<D>::JointDataDerived, same for Model.

Conflicts:

	CMakeLists.txt
	src/algorithm/center-of-mass.hxx
	src/multibody/model.hpp
	unittest/CMakeLists.txt

[C++] The stack of joints model & data is now of type joint accessor ( i.e the derived types are encapsulated in a generic joint accessor

Conflicts:

	src/multibody/model.hpp