events+ctl: freeze-thaw events implemented
Freeze/thaw functionality implemented. It is based on skipping processing of some event types (load, refresh, update, flush, dnssec), leaving them planned to past timestamp. After thaw, they are processed immediately except for updates which were REFUSED.
With this MR, please consider improving zone-status command with the information if the zone is frozen - for easy implementing scripts using freeze feature!
(Fixes #283 (closed) )