Add 'paypal-sdk-merchant' gem
`rails g paypal:sdk:install`
Add 'paypal_status' integer to Payments
Use Payments' 'paypal_status' as an Enum
Validate presence of orders on Payments
Define default_url_options for development
When destroying a Payment, disassociate it from its Orders
PaymentsController, Payment#set_express_checkout_details, Payment.set_express_checkout, Payment.do_express_checkout_payment
Store PayPal configuration in environmental variables
Move Paypal button to CartHelper
Dashboard!
Permit :contact_ids parameter in GroupsController
Show contact check boxes in group form
Remove links from GroupController#show table
Show number of contacts on GroupController#index
Show number of contacts on CartController#index