id: keep ids server-owned

[aberoham]

Every create schema accepted an id, so a caller could choose an auto-increment
value and the store would honour it:

POST /zone_record {id: 999111, zid, owner, type, address, ttl}
-> 201, record created with id 999111

POST now forbids id for group, nameserver, permission, user, zone and zone
record.

zone_record.PUT inherited an optional id from the v3 object. Every other
PUT schema names its fields and never listed the key. An update reads the
record named in the URL, so an id in the body is at best ignored. In api it
was worse: the handler merged the path id first and let the body overwrite it,
so the write landed on a record the caller never named. NicTool/api#71 fixes
that order. Refusing the key here closes it whatever the handler does.

The v2 REST bridge sends no id in a PUT body. Transport/REST.pm deletes the
path parameter from the call vars before it builds the body. The multi-put path
serves only the move actions.

Ids belong to the store. Defining that here rather than in the api means every
layer inherits it, instead of each one remembering to strip the field.

Ticks "verify the API won't permit setting auto-increment fields" in
NicTool/api#6.