Mention cancelling an event can not be undone, hide cancel button after cancelling

[danieldegroot2]

Observed
Cancelling an event can not be undone. Users are not aware of this.

When an event has been cancelled. The 'Cancel event' button is still available, but non-functional.

Expected
Users are made aware cancelling can not be undone. Cancel button is hidden after cancelling.
(or cancelling is allowed to be undone)

[thomersch]

Probably, more logically, we should make it possible to "uncancel" an event, right?

[danieldegroot2]

I mentioned this between brackets already in the main post. Feel free to edit the issue's title if needed.