Provide default configuration for air-gapped environments

[ayjayt]

Plotly by default uses CDN's for it's basic javascript includes, these won't work in airgapped systems.

Cache them in the directory so that those are used instead.

[ayjayt]

Kaleido/src/py/kaleido/_page_generator.py

Lines 12 to 15 in d93391e

	DEFAULT_MATHJAX = (
	"https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.5/MathJax.js"
	"?config=TeX-AMS-MML_SVG"
	)

[ayjayt]

This is in testing.

[ayjayt]

Also, check that we're properly transforming Path to uri's when doing custom pages, related