Remove triplestore -> jsonld dependency

[mguihal]

Hello,

I'd want to start a Moleculer Semapps instance with just the triplestore service (just accessing database to do queries), but the triplestore service has an undocumented dependency to jsonld service, which has recursively dependencies to api service, and ontologies service. It would be nice to be able to start a database adapter without having to declare 3 others services, with api and port required.

The only reference to jsonld inside triplestore service is here: https://github.com/assemblee-virtuelle/semapps/blob/master/src/middleware/packages/triplestore/actions/insert.js#L35-L40

If I understand well, this serves to format RDF query from provided json object, and adding correctly prefixes from ontologies.

I don't know how we can manage to remove this dependency without breaking the feature, except make the jsonld service dependency optional and throw an error if we try to call it if not defined, or otherwise we can try to reimplement the logic of RDF conversion from jsonld service inside the triplestore service (but it's not so easy, as it also manages a local cache and so...).

What do you think?