Drop OWL property types

[kcoyle]

The vocabulary definition today uses OWL property types to define some of the properties:

<http://example.org/openWEMI/manifests>
  a owl:ObjectProperty ;

Note that some properties that were added use RDFS instead:

<http://example.org/openWEMI/relatedItem>
  a rdfs:Property ;
  rdfs:label "related item"@en ;

It has been suggested that, to the extent possible, we use only RDF/RDFS. Should we define all properties as rdfs properties, removing the OWL property definitions?

[kcoyle]

Decided June 21 to use rdfs.