Remove pylode because Marie says she was only using it for the HTML
docs, but I'm doing that differently now. This means we can have a
direct dependency on rdflib now.
Also, move isort and black to dev dependencies because nobody will
need them except me. :)
Currently covers the dependencies used in Marie's Jupyter notebook
and some extra dev tooling. Note that I had an issue using poetry
to install pylode, so I added it to pyproject.toml manually.