the getFaces method assumed dim to be always 3 and refused interface
faces with less then 3 vertices. For dimension dim, a face has at least
dim vertices, e.g 2 for dim == 2.

This makes it possible to use the DuneEnableAll marcros with dune-mc and
python-tpmc.

The threshold functor has to be initialized before the marchingcubes
class.

Instead of filling the vector with dummy geometries, we use the
std::back_inserter in order to insert the correct geometries directly.

* remove obsolete marchingcubes refinement
* debug tpmcrefinement
* reintroduce the removed NonDegeneratingThresholdFunctor, no in a
  separate file