Feature/add python bindings

As discussed at the developer meeting (in 2018) the Python bindings are being moved from dune-python into the core modules. Corresponding merge requests are open in dune-geometry, dune-grid, dune-istl, dune-alugrid, dune-spgrid, dune-polygongrid and in dune-fem,dune-fem-dg,dune-vem

I want to merge this quickly because rebasing all the merge request will get more involved the longer I wait. @all so if there are any comments please let me know