Lazy Streaming of Tabs

[jakeatgalileo]

[Jupyter Lab is problematic but pushing for now]

Overview + Changes
The frontend first loads in the first tab on initialization. Then, it listens for changes on a variable to see when tabs are finished. I also refactored some code for better readability.

Backend PR: lux-org/lux#291

Only tested on Jupyter Notebooks as I will be working on Jupyter Lab 3 compatibility next.

Example Output

[jerrysong1324]

Hi Jake, curious how this changes the toggling between Pandas and Lux. I think it's done now as tabs instead of as a button. Can you point me to where that toggle is handled? I wish to add logging for that. Hopefully, I can add that in directly and merge it in with your PR?

Another note is I made a lot of changes as well to widget.tsx in #72 so let's be careful when we merge these PRs not to override anything.

P.S. Only did a quick review and look over, if a more thorough one is desired from me, please let me know and I'd be happy to do so.

[jakeatgalileo]

@jerrysong1324 Hey so the tabs is actually in the backend here: https://github.com/lux-org/lux/pull/291/files#diff-b3f5355f16af7450f6bf0669466ac57ae020ed8c0a56105e8ece9c8c035a8879R644. I was using the built-in tabs from the Ipywidgets library

[jerrysong1324]

#72 is already merged in (and caused new merge conflicts sorry), so when you have this ready to merge again, I'll relook to make sure my changes aren't overriden.