cekees/add cgal python

Added  the CGAL python bindings. The cmake-based  install is a little strange, but this is  working for me. @johannesring these might be useful for fenics. I'm guessing CGAL is mainly useful from C++, but I'm exploring the python bindings.
Ok. We can start with this design and we can update it later once this is merged. I still think only depending on `python` in this package as well as any package that depends on it would solve it, but I currently don't have time to try this myself, so I am fine with merging as it is, and we can revisit later.