Add Single-User Authentication

[thieman]

Spun off from #5, see original discussion there.

This issue concerns adding a single-user auth model to protect the Dagobah web client from unauthorized access. This would take the form of denying access to all web client functionality before the user has logged in. Since there would be only one user, this would not add any sort of true user-level permissions on any aspect of the service.

[thieman]

@MichaelMartinez @jonathaneunice Would like to hear your thoughts on the single_auth branch if you find yourself with some time. It's definitely a simple implementation; would you feel safe putting it up on an untrusted network in this state? If not, what else do we need to do to get it functional?