Deprecate some more Graph API surface

[ashleysommer]

Deprecate some more Graph API surface that will be removed in RDFLib 6.0.0

[ashleysommer]

Can't merge this yet. A lot of tests are failing.
Turns out some parts of rdflib (like a lot of tests) do from rdflib.graph import RDFS
With RDFS removed as an import here, those locations now fail.
I'll update this soon.

[nicholascar]

Turns out some parts of rdflib (like a lot of tests) do from rdflib.graph import RDFS

Yes, I've seen this and occasionally have done that myself, by mistake. It would be good to update everything so that RDFS, along with all namespaces are always imported from the same place, rdflib.namespace, not rdflib.graph. Good to finally address this small niggle

[ashleysommer]

Ok, turns out I was wrong. It wasn't used in the tests, but in the inline doctests in graph.py, I didn't know Travis tests those too.
I've updated those so should pass tests now.

[coveralls]

Coverage decreased (-0.06%) to 75.496% when pulling 2fc55b3 on deprecate_graph_api into 1a70666 on master.

[coveralls]

Coverage decreased (-0.06%) to 75.496% when pulling 2fc55b3 on deprecate_graph_api into 1a70666 on master.

[coveralls]

Coverage decreased (-0.06%) to 75.496% when pulling 2fc55b3 on deprecate_graph_api into 1a70666 on master.

[ashleysommer]

All tests pass, good to merge 👍