Make the embedder url configurable

[SylvainCorlay]

This would be useful to have a local use of the extension that use another URL for the javascript.

As per conversation in #3 .

[mpacer]

If this is going to be configurable here, we probably should also make it configurable in nbconvert, yes?

[SylvainCorlay]

Sorry I did not respond to this. +1 on making it configurable globally.

[infinity0]

Could we please think about this sort of thing (being able to use local copies rather than downloading everything) before release? For jupyter in general I mean, not just this project. Otherwise it makes packaging this for Debian more painful. And it is already incredibly painful due to all this NPM crap.

[maartenbreddels]

#16 makes this configurable actually, so merging that could close this issue.

[jasongrout]

Closed by #16.