zone-events: issue zone notifications after zone file change
If the events are serialized, we could have a single point where a zone change is detected and notifications are scheduled. As a temporary precaution, I've filled in the notifications scheduling after DDNS and resign in the commit 22db 1f90d But this is not fixed in master branch and the purpose of this issue is a reminder that it should be solved in the # 209 in a better way.