Add bindings for rdflib namespaces. Import DCAM.

[edmondchuc]

Fixes #1470

Proposed Changes

• Add bindings for rdflib namespaces.
• Import DCAM to be available in the namespace package.

[nicholascar]

Oh dear, this seems to have broken a couple of SPARQL tests!

[edmondchuc]

I have no idea how adding these additions would break the SPARQL tests. I'm keen to look into it if you have any ideas @nicholascar.

[nicholascar]

Perhaps the breaking is due to testing that uses a fixed set of namespace PREFIX statements in the SPARQL?

[edmondchuc]

@nicholascar I fixed the tests.

Essentially what I did was change the SPARQL service queries for DBPedia's URL from http to https and now it works.

PREFIX ex:<http://example.org/>
select ?s ?p ?o
where {
     SERVICE <https://DBpedia.org/sparql> {
        VALUES (?s ?p ?o) {(ex:a ex:b 1) (<http://example.org/a> <http://example.org/b> 2)}
    }
} 
LIMIT 2

No idea why the http version works fine with the basic prefix bindings (rdf, rdfs, etc.) but did not work for the others 🤷‍♂️.

I think it is fine to make this change to the service query URL since it's a functional test to an external service.