Fixed zone node list in zdb and empty response.

zdb_create_list() was inserting the nodes in reverse order
  (ldns_rr_list_pop_rrset() pops LAST RRSet, not first!).

Empty response was used for responding to all queries, though
  it lacked data copied from the query. Now copies ID, Question,
  and RD bit if a query is given.

Added a lot of debug ouput in zdb.
Added delegation point and glue A records to example zone file.