move libknot/zone/* into knot/zone/

Knot.files

src/Makefile.am

src/knot/server/notify.c

src/knot/server/notify.h

src/knot/server/rrl.h

src/knot/server/server.c

src/knot/server/server.h

src/knot/server/zone-load.c

src/knot/server/zone-load.h

src/knot/server/zones.c

src/knot/server/zones.h

src/knot/zone/estimator.c

src/knot/zone/node.c

src/knot/zone/node.h

src/knot/zone/semantic-check.h

src/knot/zone/zone-contents.c

src/knot/zone/zone-contents.h

src/knot/zone/zone-diff.c

src/knot/zone/zone-diff.h

src/knot/zone/zone-dump.h