Item classes

Item classes are trivial catalog objects, as they contain no fields at all, except for their names (and editor comments, but those aren't real fields).

Item classes are used by item containers and items, to simulate different inventory "slots" and limit placing items in them. Each item has exactly one class, while each container slot can be able to contain any number of different item classes. (For example, a hand slot could be set to allow sword, axe and staff item classes.)