Unique assocation end constraint should not consider non-navigable ends

[Matthias Schoettle]

When checking for unique association end role names, only navigable ones should be considered.

A (myA) <--- (myB) B and A (myA) ---> (myB) SomeOtherClass will fail, even though only one is visible/navigable.

[Céline Bensoussan]

Resolves #363: Update AssociationEnd constraint so that it will only check navigable association ends

→ <<cset 6a1ee147116f>>