Static file mounting

This begins the adventure of both:

* Sticking nginx in a container
* Mounting static assets from the userland container to the nginx container

This also tosses the `static.tar` legacy file.
Hmmm, with that I'll need to start a new nginx container too then (so that it links to new static assets).

I'm not as worried about upgrading nodes in place since we can end up with a version mismatch here:

1. User creates a notebook server
2. (Some) assets are cached by their browser
3. We upgrade the static files served by nginx
4. They open a link to their server on a different browser, computer, etc.
5. The notebook now uses different js/css than is served by nginx