add a tag 'catalog record' into the triplestore

[pvgenuchten]

Currently we have a number of types of resources in the triplestore, each with their own type (dcat:dataset, eurio:publication, oaf:work) each described using dublin core properties. In order to query the catalogue for any type, maybe an idea to add a tag 'catalog record' for each of these resources into the triplestore

Originally posted by @hugodegrootwurnl in #24 (comment)