Add paypal backend
Remove PaymentItems and Contact models
Ignore eggs
Add PaymentItem and redirect exception
Add some extra fields into the payment model
Implement new paypal api

TODO: save extra data into payment, add token into redirect_url
Remove unnecessary variable, PEP8
Add requests into requirements
Add payment token
Paypal refactoring, execute payment
Add default endpoint in paypal
Paypal refactoring
Require payment object in the provider init
Return payment response not data
Require provider and payment in base form
Add paypal credit card payment
Add authorize decorator
Configurable Payment model
Improve Paypal status management
Use status_changed in Paypal card