Replace custom hasher with std::hash specializations

[jagerman]

Right now we have several data structures that have their own Hash class which has to be used when putting the type in an unordered_set/unordered_map, such as std::unordered_set<T, T::Hash> or std::unordered_map<T, V, T::Hash>. It would be nicer if we converted all of those to std::hash<T> specializations so that we could just write std::unordered_set<T>.

[majestrate]

this should be fixed, i need to verify it.