Add inverse of skos:member

[sroertgen]

Currently there is no link from a concept or concept scheme to a collection. That is by design in SKOS. Though we now have information in the HTML that is not represented in the JSON data. @acka47 already noticed and mentioned this:

I know, there is already a PR at #200 but I have to add some information her efor the sake of completeness.

As there is no inverse for skos:member we will not be adding it to the concept's JSON-LD.

In a direct correspondence with @solth, I hinted to a solution for this but missed to post it here. Generally, I assumed that the HTML is built from the underlying JSON so that we might need the JSON-LD statement at skos:Concept pages that a concept ist memberOf a collection. We could add this as JSON-LD supports reverse properties. Basically, we could add to the JSON-LD context something like this:

{
   "@context":{
      "memberOf":{
         "@reverse":"skos:member"
      }
   }
}

This would enable adding those statements to the JSON-LD, e.g. in https://test.skohub.io/acka47/testing-skohub-vocabs/heads/master/w3id.org/kim/hcrt/assessment.json:

{
  "id":"https://w3id.org/kim/hcrt/assessment",
  "memberOf":"https://w3id.org/kim/hcrt/test_collection"
}

Originally posted by @acka47 in #159 (comment)