[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

[Minor] Update name in Data of oMof to oMf + in frames algo get directly the value of the parent joint when the relative placement of the frame wrt parent joint is Identity

[C++] Added type of Frame JOINT. Even if it is a redundent information, add a frame for each joint added

[C++] bodies are now a subpart of the Frames : some Frames are of type BODY and when referring to getBodyId/Name in Model it will look in its frames

[C++] Fix multiple bugs such as getting the correct name of geometryObjects, or initialize the bodyParents vector correctly, + binded some model datas