- Most changes were in ddns.c: Empty checks used rr_count == 0

- RR insertion function now returns zone RRSet.
- Removed reduntant zone contents / node API functions
- Cleanup.

- Fixed mismatched variables, do not use call directly in for loops.

- previously static function 'put_rr' in internet.c has been made public, it handles additions of RRSIGs as well now, by adding the to a list that is traversed after each section has been solved.

- Removed rrset->rdata_indices, RDATA lengths are now stored inline together with RR's TTL
- Added function to get RR's TTL - TTL of the whole RRSet can still be obtained, but it will default to the first RR's TTL or 0
- Renamed few RRSet functions, removed a few too - the file still needs a cleanup and function reordering
- Special handling for RRSIGs during AXFR-out no longer needed (yay)

Conflicts:
	src/knot/ctl/knotc_main.c

- Removed hattrie for duplicated DNAMEs - was not active anyway.

Ipv6 Is Not A New Thing

Most is said in the commits.
The basic idea is to reuse the (already provided) structures and streamline in the xfr-handler and server/zone structures in preparation for the zone events.

Conflicts:
	src/libknot/tsig-op.c

Conflicts:
	src/knot/server/xfr-handler.c
	src/knot/server/zones.c
	src/knot/server/zones.h

Forwarding Fix

Correct message id reinstating, appending of TSIG RR when forwarding query/response.

Zone Loading Failed Diff + test cases

See the commit messages, should be clear.
Also, the `failed to sign the zone:` message appears also when ixfr-from-differences fails, because it's together in one function (so it prints out even if I don't have DNSSEC signing enabled).
I'm not sure how to handle this properly, maybe have differences and zone signing in a separate functions and print the reason from within.

covered:
- data change, serial increase
- data change, serial doesn't change
- data change, serial < initial serial

zone