Add IRI for namespace in RDF serialisations

[coolharsh55]

Hi. The RDF files do not specify what is the IRI of the vocab in the file itself. e.g. interop.ttl does not specify namespace IRI in the prefix (<#>) or the vocabulary description (<>) or the definition of terms (rdfs:isDefinedBy <>). So once downloaded, there is no way to figure out what's the IRI. Though there is a prefix interop, it cannot be assumed to be the IRI.

PREFIX : <#>
PREFIX interop: <http://www.w3.org/ns/solid/interop#>

<>
dcterms:issued "2020-06-14"^^xsd:date ;
dcterms:modified "2020-09-24"^^xsd:date ;
rdfs:label "Terms for application interoperability in Solid"@en .

:Agent
  a rdfs:Class ;
  rdfs:comment "An agent profile for the Solid Ecosystem"@en ;
  rdfs:isDefinedBy <> ;
  rdfs:label "Agent"@en .