Fix limbo state

This is not a perfect fix, but it mostly resolves the issues in #187. When visiting a shared article, visitors in non-active statuses will see the guest view. The only weird caveat is that they will also see the navbar (Which just says "Practicing Ruby" and "Sign out". I am having trouble thinking of the right behavior.

Really, the good solution would probably be to have a third view entirely, one that replaces the share banner with a notice like "Resume your registration" or "Go back to the home page". But I'd like to get a stopgap measure out there for now.

Keep in mind that this only affects two groups: 1) people who attempt to visit shared articles *after* initiating a signup process but *before* finishing it. 2) People with expired accounts who are *logged in* and attempt to visit a shared article.