Track updates to zone for catalog zone processing and incremental zone-verification

[wtoorop]

The PoC implementation was based on the zone-verification feature of NSD and compared the complete Catalog zone with the zonelist file.

This is a good spot on AXFRs, but with IXFRs we would rather process the individual IXFR messages as comparing the whole zone data could become slow for large zones.

• [x] #256
• [x] #257
• [x] #258