iPython Notebook viewer for GNOME Sushi

I made a .ipynb notebook viewer for gnome-sushi, which I'm releasing into the wild as this GitHub Gist (under the GPL per the original).

Update 2020: Thanks to a recent pull request, this can now be installed by placing it in ~/.local/share/sushi/viewers.

Known Issues

• Slow
• If for some reason you don't have write access to /tmp, you're gonna have a bad time (can be ameliorated by changing the tmpdir constant)
• No thumbnailer (seems like a lot more work needed that I don't have time for right now — note to self: https://developer.gnome.org/integration-guide/stable/thumbnailer.html.en)
• Without internet access, will only display a white screen. This is because
  • Jupyter nbconvert uses MathJax, JQuery and require.min.js, which are externally hosted (but dumps half an MB of CSS into the preamble anyway). If any of these resources returns a 404, the WebKit webview crashes.
    • This is also why I create a file custom.css in the tmpdir. I could alternatively remove references to things with some sed/awk magic, but then e.g. $\LaTeX$ would break.
    • Interestingly, 404's returned from CSS urls (e.g. fontawesome) don't crash the webview.
• I'm assuming a MIME-type of application/x-ipynb+json — change as necessary.