WWTMVC5: skip the login rigamarole for the root index page
WWTMVC5: skip the login rigamarole for the root index page

I'm finding occasional NullReferenceExceptions on the index page,
related to the Live auth. I can't track down what's causing them but
they don't appear to be anything resulting from actual, real-world usage
of the app. And my actual, real-world usage seems to work fine. So the
simplest way to get these errors to stop popping up in my telemetry, I
think, is to just skip the auth stuff here. It's not needed anyway.

WorldWideTelescope/wwt-website,WorldWideTelescope/wwt-website,WorldWideTelescope/wwt-website