Add a logout button

[gauntface]

The Problem

When project health gets in a bad state with GitHub, there is no way to force a fix (I had to revoke the OAuth application for testing some stuff unrelated to project health).

Expected Behavior

Have some way to logout (footer text, nav item or ...)

[samuelli]

How should this behave exactly? For example, we could clear all the client side cookies, which is an effective logout, but when you load project health, it will auto-redirect to GitHub auth, and since it's already been authorized, you'll just log back in (going through all the auto-redirects).

Is that sufficient? It seems like if we had an full login page (that links out to GitHub), you'd get back to the login screen better.

[gauntface]

Thats the assumption - that GitHub is already authed. If I disallow the project-health github app, we get in a weird limbo state of an empty dashboard, red heart and no way to go through the auth flow where I wouldn't be authorized.

Someone mentioned they liked the idea of the index page doing nothing more than redirecting to either a login page or a signed in page meaning you can always get to either page if you want to link to it.

But yes a login screen would have been perfect.