Switch to the new extension distribution system

[jtpio]

Fixes #32

This was bootstrapped from the TypeScript cookiecutter: https://github.com/jupyterlab/extension-cookiecutter-ts

Then:

• removed TypeScript files and TypeScript related scripts
• removed the optional server exension
• added lib/index.js

Can be tested locally with:

mamba create -n test cookiecutter nodejs python  -y
conda activate test
cookiecutter https://github.com/jtpio/extension-cookiecutter-js --checkout packaging

[jtpio]

Since quite a bit of the boilerplate code now comes from the TypeScript cookiecutter, it would be nice if the JS cookiecutter could somehow "inherit" from the TS cookiecutter (which is more actively maintained), and only keep the JS relevant parts.

[jtpio]

Alternatively, maybe the TS cookiecutter should actually support JS too? When prompted, the extension author could choose between a JS or TS extension (defaulting to TS):

• if JS, then the lib folder is created
• if TS, then the src folder and other TypeScript related files are populated

Which means the https://github.com/jupyterlab/extension-cookiecutter-js repo could simply be archived in favor of https://github.com/jupyterlab/extension-cookiecutter-ts.

[blink1073]

Looks like inheriting cookiecutters is not yet possible: cookiecutter/cookiecutter#1485

[blink1073]

Thanks!