API: Support adding records/comments at zone creation

API: Support adding records/comments at zone creation

Records and comments can now be supplied at zone creation time;
a given SOA record replaces the automatically generated SOA.
If no nameservers are given, we assume the user supplied NS
records as well. (This now allows creating a zone without
NS records, which may be useful for slaves.)

Default SOA serial is now 0 to match other parts of PowerDNS.
SOA-EDIT-API is now honored at creation time.

Fixes #1379.
Fixes #1376.