Removes automatic unset_volunteering

Because AnthroCon doesn't let people select their own departments, the
confirmation forms never passed through the attendee.staffing variable.
This hides the check for .staffing behind COLLECT_INTERESTS, so uber
stops automatically resetting the badge type to Attendee.
Display badge combinations

Displays all badge combinations depending on what badge an attendee has.
Also displays the right badge price in some cases, but not all.
Display correct price based on paid status

Checks if the attendee has paid or is marked as not needing to pay.
Moves the payment logic from badge_choice to the javascript in
preregbase.
Forces amount_extra to 0 if it's too high

Changes the amount_extra to 0 if it goes over the Super Sponsor price.
We should fix the core problem of the session going off kilter, but this
is a stopgap until then.
Actually fixes amount_extra

Makes amount_extra a hidden input field instead of a select field,
according to COLLECT_INTERESTS, so the code to change it doesn't go out
of whack.
Correctly disable badge boxes

Moves the check for amount_paid so it always runs, regardless of what
the amount_extra field is.
Merge pull request #799 from magfest/fix_confirm_page

Fixes for the confirmation page