Introduce python function for adaptive refinement
requested to merge lnebel/dune-gfe:feature/add-option-to-run-film-on-substrate-without-any-shell into master
With this, the preparatory stretching experiment for film-on-substrate can be done using dune-gfe. The vertices for adaptive refinement can now be selected without specifying a shell area.
@osander: Can you have a look please? Thanks!