Adopt RDF/JS library (pending ES module support in VSCode)

[RinkeHoekstra]

Adopting the RDF/JS libraries has benefits over using Oxigraph and rdflib.js.

• It allows for more finegrained control of rendering, and supports the preservation of namespace prefixes when converting from one format to another.
• It supports TriG

Current blocker is the lack of support for ES modules in Electron, and consequently VSCode. This means that we cannot import any of the RDF/JS libraries natively as this requires an unsupported dynamic import.

Until VSCode and Electron support this.