Feature: Read RDF input from a URL

[jaw111]

It would be handy to allow reading the RDF input from a document URL similar to what is supported in the JSON-LD Playground.

This would allow users to reference RDF documents on the web, as well as RDF results from a SPARQL endpoint (e.g. CONSTRUCT or DESCRIBE results).

Requests to the URL should add all supported RDF media types in the Accept header in the HTTP request and figure out the response media type based on the Content-Type header in the response. The RDF could be rendered in the input box and made editable or kept read-only, but need to see if this is reasonable if the RDF document is large (or not pretty-printed).