mark donation as canceled and send email confirming the cancellation.
Can only be called if utoken is not expired.
Request model parameters:
- Cancellation status (currently it's 'ok', 'error', 'done' and 'echo'. What they mean needs more explanation). The status determines the result page.
- donation ID
- if status is 'ok', another field showing if sending the mail was successful (success page must be shown, even when the mail was not sent).