[C++][Python] Removed references to kinematic model/data in geometry model/data. + fixed unallocated memory map ( due to using reserve keyword instead of resize)

[C++] Removed type from GeometryObject. Still using the enum GeometryType to specify if visuals or collisions must be parsed from urdf file

Conflicts:

	CMakeLists.txt

[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

[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

As it is done in src/multibody/parser/python.cpp, one can create a shared_ptr to a new Model in c++,
send this into a python namespace, update it in python, and continue to work on the Model in c++.

An example to use this as a simple parser is given in unittest/python.cpp and models/simple_model.py

(squashed version)

With next version of Eigen3, it seems that there exists a missing
initialiser when calling the cast operator.

[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++] Make distinction between joint and body in Model API ( addJoint, appendBodyToJoint, addJointAndBody instead of addBody)

 [C++][Unittest] Reworked JointAccessor Unittest. tests are now done on every type of joint of the boost variant Model