Clean ConceptScheme identification logic

[rob-metalinkage]

Its OK to use namedGraph URI for vocabulary if no other clues exist, but this should be overridden by either skos:inScheme or skos:narrowerTransitive (implicitly) of skos:topConceptOf relationships.

Furthermore its possible for a Concept to be a member of more than one scheme. This will need to exploit the existing breadcrumb logic to highlight the "current scheme of interest" and links should be provided for other schemes found.

Consideration should be given to rdfs:isDefinedBy if a specific scheme needs to be highlighted as a "master" - i.e. the governing register function for that identifier.