Improve Ddns Tests

- Every scenario from old tests rewritten, plus some new ones added, some are still failing

Rrset Free Remove

I'm not sure if this will conflict with some of your work, if yes. we'll cancel this.

- nodes were marked as empty, but the information was never used ...
- renamed one function for clarity.

Fixes #218

Log Control

refs #222

DDNS tests for new test suite

Include config.h

The config.h is now implicitly included using -include option of the
compiler. After this change, config.h need not be placed at the first
position in all source files.

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

Conf Optimization

Auto Retransfer

refs #220

*14.102.145.in-addr.arpa. is valid dname (no wildcard!) but evident typo

refs #220

 - random test used for chain fix testing
 - manual test, some of the cases copied from the old tests, but not all.

Signing after UPDATE fixed

Fixed changeset signing after UPDATE.

Was ignoring RRSIGs related to a RRSet that was completely removed. This was a relict of old code when RRSIGs were connected to their RRSets.

Also simplified the function (and function `sign_rr_should_be_signed()`) and did some minor refactoring and polishing. Please try to check if function `sign_changeset_wrap()` is equivalent to its previous state.