UI: add support for platform URLs

[agarciadom]

At the moment, the EMC RDF driver does not support platform:/ URLs when running from Eclipse. This is because we pass the URL directly to Jena, which doesn't understand those. We may need to either figure out how to add platform:/ support to Jena itself, or to have the Eclipse developer tools use a subclass of RDFModel which preprocesses those platform:/ URLs and resolves them to absolute filesystem paths.