jupyter: export to pdf via html

[williamstein]

Constantly people make notebooks that nbconvert (etc) can't convert to pdf, for various reasons, including latex errors, incompatibilities, lack of network access (trial users), etc.. The one thing that ALWAYS WORKS though is to print to html (which uses our react backend renderer), then use your browser to print that html to pdf.

If printing to pdf fails for any reason, we should provide an alert box that suggests printing to html. It should include a button that prints to html then opens that html in a new tab and activates browser print on it.