Bug 1095868 v2 clickable progress dots

Here's another way we can make clickable progress dots.  I personally favour our [v1 solution](https://github.com/mozilla/bsd-forms-and-wrappers/pull/16) than this as this has to deal with `pushState` and that alters browser history even more - this seems to make things more complicated.

Either way we'll still have to fix the issues with clickable progress dots + browser back/forward button madness.