Upgrade doc dependencies, including sphinx-rtd-theme 0.5.0

[huonw]

Upgrades:

• sphinx-rtd-theme 0.5.0 gives us slightly nicer display, and helps with Demo notebook navigation would be easier with more information in side-bar ToC #1499 (there's built-in styles for deeper table-of-contents sidebars: Allow the sidebar ToC to be deeper #1512).
• nbsphinx 0.7.1 includes the fix for Output images are fractionally too large for their container, in Safari spatialaudio/nbsphinx#452, which affected all of the plots in demos
• other upgrades are just nice-to-have without particular bug fixes in mind

Rendered: https://stellargraph--1722.org.readthedocs.build/en/1722/

Notable improvements:

• nicer display of function parameter docs (etc.):

  • before: https://stellargraph.readthedocs.io/en/v1.1.0/api.html#stellargraph.StellarGraph.edges
    
  • after: https://stellargraph--1722.org.readthedocs.build/en/1722/api.html#stellargraph.StellarGraph.edges
    

• glossary:

  • before: https://stellargraph.readthedocs.io/en/v1.1.0/glossary.html
    
  • after: https://stellargraph--1722.org.readthedocs.build/en/1722/glossary.html
    

• scrolling of images in notebooks, in Safari:

  • before (hover over the history plot and scroll): https://stellargraph.readthedocs.io/en/v1.1.0/demos/embeddings/deep-graph-infomax-embeddings.html#Model-Creation-and-Training
  • after: https://stellargraph--1722.org.readthedocs.build/en/1722/demos/embeddings/deep-graph-infomax-embeddings.html#Model-Creation-and-Training

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[timpitman]

I wonder if we should make a point in the release checklist to address this regularly - eg just after each release (to minimise risk) we could upgrade all the doc dependencies?

[huonw]

That's a good idea! I won't add it here, though, in the interests of getting this merged now.