Inbhir Nis (Inverse navigation fixup)

When a navigation is changed the inverse will now be fixed up to match.
Less navigation; same destination... (Remove NavigationAccessor and its cache)

We were previously looking at the CLR type of the navigation to determine whether it was a collection or not. Now we're using the IsUnique metadata from the foreign key. This means that the CLR type info caching for navigations is not required anymore.