Handle silent logouts (expired authentication) more gracefully in the Argo UI

[andrewjbtw]

When users are logged out of Argo after periods of inactivity, many buttons and links silently stop working. This generates confusion when functions on the show pages stop working because they require authentication. For example, many of the red buttons that carry out actions or pop up modals don't do anything if you are logged out - there generally isn't even an error message. The sections of the page that expand or collapse also don't operate as expected.

Argo should handle this situation more gracefully, either by presenting some feedback that indicates the user needs to log back in ("You have been signed out, please reload this page"), or by triggering re-authentication automatically, as happens when someone reloads the page or clicks on links to new pages.