extraction sample in turtle-triples should use prefixes

[VladimirAlexiev]

(A simple warm-up task)

See eg http://mappings.dbpedia.org/server/extraction/en/extract?title=Great_Britain_men%27s_national_basketball_team&format=turtle-triples&extractors=custom . It's very hard to read because it doesn't use prefixes.

Add as many common prefixes as possible, so the listing is more readable.

• See http://prefix.cc/dbo,dbp,dbr,rdf,rdfs,foaf,dc,dct,skos.ttl for a start
• For instances use dbr: dbrfr: dbrit: etc
• For raw props use dbp: dbpen: dbpfr: dbpit: etc