Move processAssociations inside the preProcessor

[Céline Bensoussan]

In the weaver, associations should be processed in the pre processing phase.

[Matthias Schoettle]

Also, when keeping the association from the user, the feature selection needs to be removed. Otherwise the woven model will point to the original model.

[Jörg Kienzle]

What do you mean by that? It needs to be removed?

[Matthias Schoettle]

The reference from AssociationEnd to COREModelReuse needs to be unset (to null basically).