Output datasets should comply to mappings

[Marco Fossati]

See #64 .
Use the DBPO mappings first.
For each entry:

• if a mapping is found, use the http://dbpedia.org/ontology/ namespace, e.g.,

<http://it.dbpedia.org/resource/Davide_Matteini> <http://dbpedia.org/ontology/careerStation> <http://it.dbpedia.org/resource/CareerStation_$ID> .

• otherwise, use these translations, with the http://dbpedia.org/fact-extraction/ namespace.