Add background to dealer pages

Adds the masthead and white background to the dealer confirmation and
group member pages.
Refactor Javascript into specific files

Moves the javascript for pre-registration pages into just the pages that
will need it.
Update group_members text

Updates the text to match AC dealer registration needs. Also adds a
background to group_extra_payment_form.
Show correct badge type when claiming badges

When claiming an unassigned badge in a group, the attendee object has no
useful information. This goes off the group object instead so it
displays correctly.
Show correct prices when claiming badges

Because attendees claiming badges in a group are new, their badge price
was erroneously displayed as the Attendee badge price. This
special-cases that down to 0.
Merge pull request #854 from magfest/fix_dealer_reg

Fix group badge claiming and display fixes for dealers