code: def add_source(self, evidence_line, source, label=None, src_type=None):
          
          self.graph.addTriple(evidence_line, self.globaltt['source'], source)
          self.model.addIndividualToGraph(source, label, src_type)
          return
docs: Applies the triples:
          <evidence> <dc:source> <source>
          <source> <rdf:type> <type>
          <source> <rdfs:label> "label"
  
          TODO this should belong in a higher level class
          :param evidence_line: str curie
          :param source: str source as curie
          :param label: optional, str type as curie
          :param type: optional, str type as curie
          :return: None