[python][cleanup] Don't specialize DimRange for nodes

The DimRange template class from dune-common is used to spezialize for range types in order to specify the corresponding range dimension. Specializing DimRange for a node seems to be rather odd. Furthermore this is only used locally in registerBasisType(). Hence we effectively abuse DimRange to sum up the leaf node range dimensions recursively.

This patch replaces the construction by a simple recursive constexpr function and by the way replaces the clumsy check for node tags by is(Leaf|Power|Composite) and introduces a static assertion for the non-supported dynamic power case.