Refs #996 @4h

refs #1103

Adding empty NSID data is completely legal. It is however a matter
of discussion if the function should add the EDNS OPTION or not.

The arguments supported are OK from the viewpoint of the function.

Conflicts:
	src/tests/libknot/libknot/rdata_tests.c

The parse_next_rr_answer() function does not require the pointer
to be NULL.

Closes #1081

+ rdata free test marked TODO.

fixes #1101 @15m

@4h

- Fixed error functions.

- Removed response module and tests for it (the server does not
  compile now, must be fixed).
- Renamed dname_table_add_dname2() to dname_table_add_dname_check().
- Removed server pointer from nameserver, replaced by generic void *.

- Also added NSD's BSD license text to descriptor.c/.h

@1h

fixes #1098