[WIP] Added resolve entities support in discrim. map

This PR is WIP. I just wanted to know if what I am doing is wrong or I can go on with tests and documentation.

This is what happens.

I have nicely the ability to define a relation using just the interfaces, and then, resolve these relations overriding the interfaces with the implementations. This resolves a big problem: Multiple implementations of one interface.

But, when you define a discriminatorMap, you **Must** define it using specific implementations, so all this flexibility gained in the relations is lost at this point.

Using a new listener, its easy to override this interfaces.

What do you think?
Sorry, what do you mean? This method can be called many times. This class can be properly refactored, but... what can a constructor be useful for?