SetBuilder in Snapshots

[Taluu]

Allow to use a different Set (an extension, or something like that) in the built-in snapshots rather than only the built-in Set.

Currently, if you want to use something else, you have to reimplement the diff method of AbstractSnapshot... Even if all it does is just changing the class used.

[Taluu]

After some thoughts, I don't think SetBuilder would fit in here (it would be rather overkill).

I'm thinking on making a SetInterface, publicize compute method and putting it in the interface.

So, instead of using the constructor to initialize the object, we would do it from the compute method.