Add support for default scope/scope overrides

I had a use case where I needed to soft-delete some seed data using the paranoia gem, which scopes everything to `WHERE deleted_at IS NULL`.  On subsequent runs, the `rake db:seed_fu` would raise an error because it would try to `find` the record, and because of the scoping, it would not find it, so it would attempt to create a new record with that id.  The id still existed in the database, and since it is a primary key, it would raise an error.

This change calls `unscoped` to ensure that duplicate records aren't added when `default_scope` or soft-delete gems are being used.