ACTION-7: Create a list of properties with non-literal values that only list expected type as URL

Saying "expected type: URL" at schema.org is a little odd, since any non-literal valued properties can be written with URL values (with or without additional inline descriptions). It would be good to know the extent to which we have opportunity to add more informative typing information. For example, the "image" property of http://schema.org/Thing can be expressed with URL, but it seems reasonable to expect an ImageObject as the type of thing the URL identifies. This action is to analyze the extent to which we have other similar situations elsewhere in schema.org.

Rough todo list: parse RDFa from http://schema.org/docs/schema_org_rdfa.html into a SPARQL store, and figure out a SPARQL query that answers the question.