nbconvert: 3rd party widgets not loading

[danielfrg]

We have the requireLoader on the HTML manager and it loads the widget from unpkg but then it cannot find the base widgets.

I am not sure how to fix this :D

Logs from a console:

Falling back to https://unpkg.com/ for jupyter-leaflet@^0.13.2
@jupyter-widgets/base.js:1 Failed to load resource: net::ERR_FILE_NOT_FOUND
18jupyter-flex-embed.js:22245 Could not instantiate widget
(anonymous) @ jupyter-flex-embed.js:22245
step @ jupyter-flex-embed.js:22016
(anonymous) @ jupyter-flex-embed.js:21997
rejected @ jupyter-flex-embed.js:21989
19require.min.js:1 Uncaught (in promise) Error: Script error for "@jupyter-widgets/base", needed by: jupyter-leaflet
https://requirejs.org/docs/errors.html#scripterror
    at makeError (require.min.js:1)
    at HTMLScriptElement.onScriptError (require.min.js:1)

[danielfrg]

It probably has to be on how the jupyter-widgets embed works, we handle those things differently here, we include it on the bundle JS but are not available for other libraries or something like that.