[functions] major rewrite * get rid of the old macro based variant * use internal base class which defines all available functions   and derive FunctionsProvider * specialize for certain dimensions * there is some boilerplate code left but I think it is far more readable   than before
[functions] major rewrite
* get rid of the old macro based variant
* use internal base class which defines all available functions
  and derive FunctionsProvider
* specialize for certain dimensions
* there is some boilerplate code left but I think it is far more readable
  than before

renemilk/DUNE-Stuff,renemilk/DUNE-Stuff,renemilk/DUNE-Stuff