Integrate theme cookiecutter

[fcollonval]

To reduce maintenance burden this merge https://github.com/jupyterlab/theme-cookiecutter

The cookiecutter variables have been changed to first request the type of extension using a enumeration: frontend, server or theme.

[jtpio]

Thanks!

To reduce maintenance burden this merge https://github.com/jupyterlab/theme-cookiecutter

+1, since the theme cookiecutter can easily get out of sync and doesn't necessarily benefit from the improvements made to the ts cookiecutter here (for example CI and releaser config).

Some follow-up steps that come to mind:

• Archive: https://github.com/jupyterlab/theme-cookiecutter
• Update the extension tutorial
• Update the apod repo

[fcollonval]

@jtpio would it be ok to move forward with this?

[jtpio]

Looks good, thanks!

[jtpio]

Some follow-up steps that come to mind:

Let's open the corresponding issues to keep track of these steps.