Note: For this DGNorm LocalFunctions need to be copy constructable.
This is true for {Mutable,Const}LocalFunctions, for GridFunctionAdapter::LocalFunction
a merge request for dune-fem is created.

- allow to use an executable with different parameter files ("test case")
- avoid overwriting of existing data folders by different test cases

This fixes the VTK output for the exact solutions for evolution problems

DomainDecomposed thread iterator.