We cannot rely on the hard-coded _versions.slim template, but this HTML must instead be generated under the shared version-bar.js file. That's because, otherwise, on every new version deploy we'd have to redeploy the old version (that adds the "this isn't current" node) as well as the new version. In addition, we'd have to redeploy every version from the beginning of time to get this watermark.

So, I'm thinking it might be easier to add a template lib with the HTML to generate, and render it if the current page is not the most recent version (which we can add a check under versions.coffee). Thoughts @lucperkins?