Use a vector instead of a range in paritition view entity set

In order to have entity sets that are compatible with the Dune::Concept::GridView , the index set should fulfill the Dune::Concept::IndexSet concept. One of the requirements of Dune::Concept::IndexSet is that Types is a random access container. Currently, this is the only part of the partition view that fails for this concept to be fulfilled. So this MR adds a change to use std::vector instead of Dune::IteratorRange. This means that a copy of the type is made every time that the method type(codim) is made. But this is a small price to pay to be conforming with the interface.