We don't allow variants to have zero weight or volume. But a DFC import
in production showed that some catalogs list products with zero weight.
Despite the products having a weight, it's simpler to treat these as
items.
I observed new data from the DFC Prototype. It now uses the DFC 1.8
ontology with the hasQuantity object.
It now also uses PUT requests for updates because PATCH is not as well
supported. Rails doesn't care though.
I couldn't observe a request for the CatalogItem yet because the
Prototype failed to send it.
