Add upgrades to confirmation pages

For AC, we're having to use kick-in levels for Sponsorship and Super Sponsorship, but AC attendees and staff understand these as actual badge levels. We had to hide the kick-in-level box, so this adds some functionality back in by displaying an upgrade selection that looks more like badge types.

Also factors out some of the JavaScript so it's centralized. A lot of this JavaScript is special-cased in order to get around very large tasks, so this will make it easier for us to fix it later on.