Update to user JupyterLab 3.0 and bundled javascript

[matthewturk]

This starts the process of converting.

Some of these items will be reverted, but using the automatic conversion on the CLI confused me enough that I wanted the web UI to view the actual diffs.

[matthewturk]

So this builds, but I'm now not able to make it run on my machine. I am actually not sure how this all works with the 4823942 versions of jupyter I have installed, etc, so I'm going to do some checking before I merge it.

[matthewturk]

I think that jupyter-widgets/widget-ts-cookiecutter#83 is relevant, because I got very confused with why the plugin wasn't working, etc. I'm pretty confident I've made a number of mistakes, but once that PR is finished I think I'll have a better basis for narrowing down the issues here.

[matthewturk]

Also I'm definitely going to squash these changes when they're ready.

[matthewturk]

Alright! Now it works. I also am able to build in place and get things to go! I had to update to the most recent ipycanvas as well as fix some dependencies, but now it's going. Yay!

[cphyc]

Just to comment that I tried this on my machine and it works if I do pip install -e . from the root folder! Hooray!