Update assets as per spree/spree#4050
Added maxipago gateway

Fixes #127
Fix BalancedGateway bug to create profile when active_marchant has changed the response of Store function for Balanced

Fixes #129
Fixes #130
Fixes #131
Switch back to using Firefox tests, as Poltergeist seems to be having issues
Include expiration in tests where Stripe is supposed to through invalid error messages for other things