Fix SPARQL endpoint

ToDo:

• Create mwo:SparqlEndpoint
• Definition: A SPARQL Endpoint is a Point of Presence on an HTTP network that's capable of receiving and processing SPARQL Protocol requests.
• Create mwo:hasSparqlEndpoint OB (domain mwo:SemanticResource, range mwo:SparqlEndpoint)
• OB definition: A relation between a semantic resource and its SPARQL Endpoint
• Change data property mwo:endpointurl domain to mwo:SparqlEndpoint