make the raw http express server secure

[williamstein]

The reason there is a scary warning message at https://github.com/sagemathinc/cocalc/blob/master/src/dev/docker/README.md
is because one can use the raw http server from one project to access any other project (whose project_id you know), since it listens on localhost. You have to scan through all ports of course, but that's not too hard. This isn't a problem for production, since in prod the raw server does not listen on localhost at all.

We should fix this by changing the raw server to secure, even in docker. That would also be generally better, since it improves security in production as well (providing two layers instead of one).

Ideas:

• Add the local_hub's secret token to the base_url that the raw server uses. Then the raw server is useless to anybody who connects to it if they don't also know that secret token. The proxy server would then modify the incoming client urls by adding that token, so all client url's would still be the same.
• Have the proxy server add an extra auth header to all requests