Calendar: Allow entering cancellation reason on meeting deletion
A follow up from:
evolution-ews#259 (closed)
The calendar with a retract capability allowed to enter cancellation text when deleting a meeting, to provide a reason why it had been cancelled/deleted. With the retract functionality gone, it would be nice to have a way to enter the reason in general, though the calendars should still have set some static capability to know when the cancellation notice has a meaning and when not. Meeting invitations/notices sent by the evolution itself, aka calendars without E_CAL_STATIC_CAPABILITY_CREATE_MESSAGES
and/or E_CAL_STATIC_CAPABILITY_SAVE_SCHEDULES
can ask for the reason always.