Create a development setup

[tomasr8]

This adds a barebones development setup that allows you to run swanhub locally. It's definitely not perfect and some things are missing but it's already quite useful. Here's what's included:

• CERN SSO integration: this is useful because you can test any SSO/Auth-related changes locally
• File watcher script: sets up symlinks and automatically rebuilds assets when source files change. This allows you to simply edit a source file (e.g. CSS or JS), save it and reload JH to see the changes applied. This is quite useful for developing e.g. the options form.

Limitations:

• Currently it just starts jupyterlab (or whatever else you happen to have installed in your venv). I want to explore using the docker spawner with our user image instead. This means you cannot use this yet for debugging/developing user extensions.