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.
What I meant is that I thought this is part of the python package -- you don't need to inherit it, you just need to depend on it. But looking at it, it doesn't seem to be part of it:
```
when_build_dependency:
  - set: PYTHON
    value: ${ARTIFACT}/bin/python
  - prepend_path: PATH
    value: '${ARTIFACT}/bin'
  - prepend_path: PKG_CONFIG_PATH
    value: '${ARTIFACT}/lib/pkgconfig'
```