upgraded iQvoc dependency
added debugging dependencies

* Zeus for faster application startup (particularly useful for testing)
* Pry & Hirb for interactive debugging
* Unicorn as server (proved to be the least problematic option)
* Cane for code quality

note that using Zeus appears to require more explicit dependency loading
revised RDF serialization

now more closely resembles iQvoc search results, using anchors for
individual results

using rdfs:label instead of skos:*Label because it simplifies the data
structure (no need to carry around labeling type) and the distinction is
irrelevant (possibly even harmful) in this context
ensured duplicate concepts are skipped in RDF serialization

a bit awkward, but effective