Add a guest mode

[jmeickle]

There should be an environment variable that toggles whether to require basic auth to view (but not create or score) proposed abstracts. People are often interested in seeing what talks might be given at an event.

[obfuscurity]

I don't think an environment variable (to toggle everything) is the right approach. If you want anonymous viewers to be able to read proposals, there needs to be a view that supports that explicitly.