Merge branch 'new-ddns' into release1.2

src/knot/server/zones.c

src/libknot/nameserver/name-server.c

src/libknot/rdata.c

src/libknot/rrset.c

src/libknot/rrset.h

src/libknot/updates/changesets.c

src/libknot/updates/changesets.h

src/libknot/updates/ddns.c

src/libknot/updates/xfr-in.c

src/libknot/updates/xfr-in.h

src/libknot/util/debug.h