Add a additional_data attr to AuthorisationResponse

Customers might require adyen support to enable this feature where their
api return the credit card last 4 digits when doing an authorization.
Should come in handy when using client side encryption and you never
have a chance to grab the cc last 4 digits
Merge pull request #86 from huoxito/additional-data-response

Add a additional_data attr to AuthorisationResponse