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

To comply with OpenNao and its BOOST version, the BOOST_TEST_MODULE
must be used as TEST_SUITE name

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)