pydeck: embed javascript for offline HTML generation

[bandersen23]

For #4290

Background

Expansion from #4400 - closed due to a better idea for the issue.
This will allow for an argument of offline and if so, will embed the necessary javascript into a script tag in the HTML file to allow for portability.

Change List

• add offline argument to bindings
• embed index.js from the CDN url into a static folder - will need to be manually updated each release.
• write function to grab binding and add it into the template.

@ajduberstein - here's an update from your idea in #4400. I manually added the javascript from the CDN, but if there's a way to automate that on build, that would make it easier when there are updates. I don't have any ideas how to do that, but wanted to flag that for you!

[coveralls]

Coverage decreased (-2.5%) to 80.683% when pulling bacb04b on bandersen23:js-embedding-i4290 into f65ac9c on uber:master.

[ajduberstein]

Thank you for your patience here @bandersen23. Verified it locally on my machine without internet access–everything works.

if there's a way to automate that on build

This should be fine for now–I'll get it documented and released in a beta.