Credit cards are displayed on the payments index.

Fixed the user#credit_card method to expand the default card argument. Added the
@credit_card instance variable back to the payments#index action.
Fixed new_card failing to update the Stripe customer's default card.
Update README
Styling for credit card form.
Merge branch 'develop' of https://github.com/tmcyf/tmcyf into develop
Updated gems and enabled jquery_ujs

Gemfile had jquery-rails but jquery-ujs wasn't enabled in application.js file. Upon clicking pay, user is asked to confirm in case of accidental payments and mindless rage.
Merged latest from develop branch.