Add support for session keys and passport.

Add ability to use session keys to sign the cookies. The way it works is
that the keys.js.example will show how the real keys.js file will look.
To use the feature just create a keys.js file in the config directory, it
won't be tracked by git. SESSION_KEY can be any long string for now. Also
add support for passport to use local authentication using
username/password combo.