Download a package's classes as an ontology file a collection takes as its own

The package's classes and relationships, in the caller's language, as the entity_types and relationship_types POST /{kb_id}/graph/ontology takes, with no packages key: applied to a collection, they become its own classes, which it edits freely. Applied to a collection that subscribes to the same package, each class is that collection's edited version of the package's instead.