R1:5bcca675e1c7

Add card expiration information to Phortune cart screen

Summary:
See PHI689. It can be difficult to distinguish between cards with the same number but different expiration dates (common when the bank sends you a new card).

For now, show the expiration date on the cart checkout screen.

Test Plan: Viewed a cart checkout screen with multiple cards, saw expiration dates.

Reviewers: amckinley

Differential Revision: https://secure.phabricator.com/D19462