rrset - move RRSIGs to node to allow RRSet refcounting
Description
Well, to allow refcounted RRSets we must relocate rrsigs and owner to the node and that's it.
This is a part of #13 (closed) and #11 (closed) .
Things completed so far:
- RRSIG synthetization from node RRSIG and covered RRSet
- Removed all extra code dealing with RRSIGs as a separate record, including removal of obsolete RRSIGs during update. (signing has to handle this)
- Unified zone load and AXFR-in, code size reduced
- DNSSEC signing (but not DDNS signing)