How do we deal with eWay restriction on Purchase action on createCardRequest

[eileenmcnaughton]

In general the createCardRequest method can do a purchase at the same time in the action is set to 'Purchase'. eWay supports this for the Transparent Redirection, Responsive Shared Page or IFrame payment methods but not the DirectConnection (which is 'RapidDirect' in the omnipay plugin).

The point of the Omnipay plugin is that the calling code should not need to know about these gateway vagaries. We have all the information within the processor to complete the purchase when the action is purchase before returning a response and I think we should do so

[eileenmcnaughton]

(I've added the above into #23)