Once the donor has chosen a payment method and clicks 'Continue', we should make an AJAX call to a MediaWiki API method to confirm the details of the payment, so if there are any errors we can try to let the user correct them.

This task is done when there is an API endpoint that makes minimal calls to
setOrderReferenceDetails ( with amount, currency, donor message, and order id )
confirmOrderReference ( makes details final, lets user know they initiated a payment )
getOrderReferenceDetails ( gives us donor name and address, checks that status is OK )

Error handling can be handled in another task.