RDF2Go integration module

This module allows to use RDF2Go (http://semanticweb.org/wiki/RDF2Go) models for (de)serialization from/to JSON-LD.

A previous implementation was https://github.com/ismriv/jsonld-rdf2go, but now it has been refactored to fit into the "integration module" structure, as discussed here: https://github.com/ismriv/jsonld-rdf2go/issues/1