Extend QHash, QSet to have an insert function that takes the hash code.

This means that in a multi-threaded application where several threads accesses a shared QHash object, you can compute the hash code without holding a lock on the container.

But there are ~15 functions that takes a key, so if we overload all of them this means a lot of new overloads. Perhaps it is better to create a thread-safe hash class (Which we one day might implement as a lock-free hash