Fetch schema.org data from DRUM

Fetch schema.org data (serialized as json-ld) in DRUM's UMD Data Collection, http://hdl.handle.net/1903/27670

JSON-LD embedded in HTML is not yet supported, see:

• Turning rdflib-jsonld into a "full processor" (a.o. for schema.org compliance) RDFLib/rdflib-jsonld#62
• Implementation of "full processor" for JSON-LD 1.1  RDFLib/rdflib-jsonld#63

[wallberg]

JSON-LD is now supported in RDFLib 7.1.0 via RDFLib/rdflib#2804