There are still some bugs inside differentiate, interpolate

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

[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++][Doc] Removed random. Changed uniformySample into randomConfiguration + Updated doc of joint-configuration algorithms. + reindentation

[C++][Python] Added a new macro for algorithms that work only with joint models instead of joint models and joint datas. Modified python binding and API accordingly

[C++][Python] Added algorithm working with joint configurations ( integrate, differentiate, interpolate, random, uniformlySample, distance), their python bindings and unittest