Sign up form changes when selecting "Is this a gift?"
-- Step 1 becomes email address, email address of recipient.
-- 2oz Trial becomes disabled
-- e-mails are sent to both parties
-- Apply Code stuff goes away
Apply Code on signup
-- Checks code
-- Shows invalid code if invalid
-- Checks e-mail address entered (warns if not entered)
-- Selects amount and interval for gift code and disables others
-- Grand Total becomes 'Free'
-- Pay with card button becomes Redeem Gift