Bug deleting cycles with analysis or AT events

[perryr16]

The relation between Event and Cycle is incorrectly set. Currently, the Event is protected when a Cycle is deleted.

class Event(TimeStampedModel):
    property = models.ForeignKey(Property, on_delete=models.CASCADE, related_name="events")
    cycle = models.ForeignKey(Cycle, on_delete=models.PROTECT)

This relationship causes a ProtectedError when attempting to delete a cycle that had Analysis or AT events.

django.db.models.deletion.ProtectedError: ("Cannot delete some instances of model 'Cycle' because they are referenced through protected foreign keys: 'Event.cycle'."

This should be changed to on_delete=models.CASCADE