Add ipytree support (Jupyter widget for tree-structured data)

[tylere]

Add support for the ipytree within Colab.

Is your feature request related to a problem? Please describe.
When working with geospatial data, there is often a need to inspect layers of information (often nested) for a region of interest. With the addition of Colab support for ipyleaflet, there is a way to display and interact with spatial data, but there is a related need to display layer data.

Describe the solution you'd like
Provide a way to install and use the third-oarty jupyter widget ipytree. A good test case would be the ability to run the ipytree_ileaflet example.

Describe alternatives you've considered
I have considered manually building simple trees using the standard jupyter widgets, but that seems like reinventing the wheel...

Additional context
When trying to display an ipytree widget in Colab, Chrome developer tools reports a 404 error accessing the following:

manager.min.js:1654` GET https://cdn.jsdelivr.net/npm/[email protected]/dist/index.js 404

I confirmed that the file is not accessible from the CDN, however, there are other related CDN files for [email protected]
https://www.jsdelivr.com/package/npm/ipytree

[giswqs]

I second the support for ipytree @martinRenou. I have a Python package for geospatial analysis called whiteboxgui, which is used by geemap and leafmap. I implemented it using both ipywidgets and ipytree. Currently, only the ipywdigets version works in Google Colab. Here is a notebook example

Implemented using ipywidgets

Implemented using ipytree

Demo

[blois]

The ipytree_ipyleaflet.ipynb example appears to work using ipytree==0.2.0:

https://colab.research.google.com/gist/blois/1af162473872445cbece540ffe6830c4/untitled1200.ipynb

The dist/ folder does not appear in the 0.2.1 release.

[tylere]

Closing since Colab support is working as intended... just need to get the CDN copy corrected.