Zone data now contains IXFR db (journal).

src/dnslib/zone.h

src/knot/conf/conf.c

src/knot/conf/conf.h

src/knot/server/journal.c

src/knot/server/journal.h

src/knot/server/name-server.h

src/knot/server/notify.h

src/knot/server/zones.c

src/knot/server/zones.h