pretty <3
added is_paypal? and is_credit_card? to contribution

Now we can identify an instance of contribution if is paypal and
credit_card payment
fix logic to define :request_refund template_name

.credits? are looking if contribution is made with credits and not a
credit_card :/
Merge pull request #880 from devton/bugfix/adjust-request-refund

Bugfix/adjust request refund