Note that there's no code for user types and fields yet -- just the schema (actually there's a tiny bit of code in the item type manager, since we'll probably use some of the same methods for managing user types, but not much)
Templates for primary item types are currently only used by the item type manager to make creating new types easier and to prevent the removal of fields from an item type that are associated with its template item type -- the fields are all still recorded in itemTypeFields, since they might have different orders or default visibility settings from their templates
