Use sparql-endpoint-fixture in graphics tests

[kstudzin]

Use sparql-endpoint-fixture to mock a sparql endpoint in graphics tests. This allows for testing the --endpoint option

Closes #100

[sa-bpelakh]

The install error it's running into can be fixed by capping the max version of setuptools to "setuptools<58.0.0", but there is still the version conflict between the other requirements. Let's talk about this Monday, we'll probably need to create an updated version of the fixture.

I also noticed you created .trig inputs for the fixture graphs, but that's not currently supported - multiple graphs are configured by supplying a graph name -> content map instead of a list of RDF files. We can add .trig support to the fixture (onto-tool itself really needs TRiG support as well, there are issues for it), but it will take time.

[kstudzin]

I'll reach out to talk about the version conflicts.

I added the trig file because it was the only way to trigger the 'single graph' clause of gather_schema_info_from_repo method. It's used to create the sparql_endpoint but I don't try to process it with the tool at all. See test_remote_graphs in test_schema.py and test_remote_show_ont_trig in test_bnode_subject.py