SPARQL Queries do not declare the XSD namespace

Due to Mulgara's automatic definition of the XSD namespace, SPARQL queries in a number of places reference XSD without defining it causing issues when switching to a different triplestore, like Fuseki.

This is potentially part of a larger issue in the way namespaces are handled, as the core fedora namespaces (fedora-model, fedora-view, fedora-rels-ext) are also presumed to be defined at the triplestore level.