`isfinite`, `isnan`, `isinf`, `isunordered` for vectors

C++ has isfinite, isnan, isinf, isunordered. It would be nice to have an overload (Dune::is*) for FieldVector and BlockVector which implement the appropriate version for vector types (where all components have to be finite, any component is nan, ...). (One can use the standard functions on the norm, but having isfinite(x) for a vector x is nicer in my opinion.) Ideally they should also work for FieldVector<std::complex<...>, ...>; the standard functions don't work for complex numbers either.