Workflow: Restore event registration cancellation

[cmutel]

This code is commented out right now.

Ideally this could be done directly from the profile page. Could we add a cancellation button which opens a modal window - that can then call a view which redirects to the profile page?

One thing to be aware of is that I have added Event.refund_last_day - if the system date is after that date, then the cancellation message needs to state that they can cancel but their registration fee won't be refunded.