use the zone delete event during zone reload
disable assert to allow freeing of zone from the delete event
utils: unify warning messages
Backported 1debc21e904ea1df13f88525aa9969a43a930dfc
events: correct way to remove replaced/removed zones
Merge branch 'zone-events-queue' into opt-refactor
edns: resolved todo
rrset: allow empty rdata
edns: fixed parsing of empty options
edns: fixed nsid, dig corrupted memory, bad memory reservation
edns: removed unused code
rrset: fixed deprecated usage of empty rdata
EDNS: Remvoved some magic numbers & repeated code
EDNS: Adding OPTION simplified.
EDNS: Fixed option adding + fixed unittests
EDNS: Some cosmetic changes.

- find_option returns uint8_t *
- Some constants improved.
Moved EDNS to libknot/rdata as opt.h
EDNS: Removed redundant printf from utils.
tests-extra: Tests for DNSSEC key events.
libknot/rdata/ --> libknot/rrtype/