Adds upgrades to the confirmation page

A rough copy of the javascript and CSS from the form page, altered so
that attendees can't try to downgrade their badge level.
Refactor JS into preregbase

Moves the javascript for badge selection into preregbase. Also moves the
international checkbox hiding function into address.html, and adds a
check for a field to get rid of our last JS error.
Fix checks for payment

amount_extra gets set before the attendee has paid, so this includes
changes to make sure the boxes are only disabled for paid attendees.
Move badge selection boxes

Factors out the badge selection boxes into the currently-unused
badge_choice template, as the html is now being used in several places.
Also adds an is_new check to make sure attendees don't try to convert
their badges to groups.
Add group_id check

Stops the "group" choice from showing for new group members. Editing a
group during registration is a little strange now, but fixing that is
really low priority.
Remove duplicate JavaScript

I accidentally left a block of JS in the address.html, even though it's
already in preregbase. Taking that out.
Merge pull request #766 from magfest/add_upgrades

Add upgrades to confirmation pages