Enhance specification description with relationships between resources

[rob-metalinkage]

The draft W3C Profiles ontology [1] is partly inspired by the need to publish interoperable metadata about two forms of relationships common in OGC domain:

1. Profiles (specifications that extend or constrain a core specification while requiring conformance)
2. role of descriptive and implementation Resources - such as schemas, guidance notes, UML etc

Implementing JSON-LD (#440 ) would allow direct incoorporation of this model to provide better information. These relationships would potentially be managed by another governance process and accessed from the definition server and just incorporated, or SDW could become the manager of this information and push it to the Defs server. The latter model is preferable and I'm ready to assist - otherwise I'll chip away at it on a piecemeal basis.

Will post some examples here when deployed to Defs Server.

[1] https://w3c.github.io/dxwg/profiles/