add dev build commands

[jenshnielsen]

And rename production build to build:prod. That matches ipympl and widget-ts-cookiecutter

With this change one can do

pip install -e . npm run build jupyter labextension develop . --overwrite

to get unminified javascript that is easier to debug. E.g. exceptions in the browser console will point directly to a readable line of js.

[github-actions[bot]]

:point_left: Launch a binder notebook on branch _jenshnielsen/ipycytoscape/add_dev_buildcommands