Mention default-soa-mail in docs

Fixes #1382.
API: Don't crash when given non-string as nameserver

Fixes #1375.
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.
API tests: rewrite test to ensure API stability

Let's test the fact that we don't need to send type/name in individual
comment entries for PATCH.
Merge pull request #1387 from zeha/api-zone-creation-fixes

API: Fixes to zone creation (Auth)