Knowledge base export

[masda70]

We want to be able to export the KB into some interchangeable format (NQuads, Trig ?)

[masda70]

Implemented by #15

To use, one can has to target the /export endpoint. The default format is TriG, however from a browser, the preferred format may be RDF/XML.

From a console, how can use curl to select the preferred format:

curl -H "Accept: application/trig" http://localhost:8080/export
curl -H "Accept: application/n-quads" http://localhost:8080/export
curl -H "Accept: application/rdf+xml" http://localhost:8080/export

Note that the KB contains named graphs, so a quad serialization is preferred. Triple formats such as Turtle (text/turtle) are supported, but obviously limited to the export of triples.