Add coupon field to XML. Remove "N/A" website fields. Update coupon and website data from Lauren's email.
Perk detail layout: Add coupon button and tweak margins
Allow websites to be optional in XML (no more truncating on missing websites)
Add 'coupon' field to Perk class and XML parser (was previously ignored).
Detail view: Add functionality to 'Coupon' button. Hide website or coupon buttons when they aren't needed.
Change some detail view background images to be more eye-pleasing (for tomorrow's meeting).