Map owl prefix in load from rdflib graph
Map owl prefix in load from rdflib graph

Fix for issue (#1341)
Missed when integrating rdflib 'owl:' was not recognised as a used prefix.
gkellogg/schemaorg,vholland/schemaorg,gkellogg/schemaorg,gkellogg/schemaorg,schemaorg/schemaorg,dbs/schemaorg,gkellogg/schemaorg,unor/schemaorg,vholland/schemaorg,schemaorg/schemaorg,unor/schemaorg,vholland/schemaorg,schemaorg/schemaorg,vholland/schemaorg,schemaorg/schemaorg,tfrancart/schemaorg,dbs/schemaorg,dbs/schemaorg,unor/schemaorg,schemaorg/schemaorg,tfrancart/schemaorg,tfrancart/schemaorg,tfrancart/schemaorg,dbs/schemaorg