Having this as an instance method makes it easier to override in the
prepended `EE` module.
If we try to override this method on the module itself, it would not
be overridden correctly, depending on the load order.
This changes the repository type from a binary `wiki?` to a type. So
we can have more than 2 repository types.
Now everywhere we called `.wiki?` and expected a boolean, we check
that type.
