Make api changes do a rectify by default, add an option to disable

Make api changes do a rectify by default, add an option to disable

Previously, you had to set API-RECTIFY metadata on every zone you wanted to
have automatically rectified on changes through the API. With this change, the
default behaviour is to do a rectify, but this can globally be cahged with the
setting default-api-rectify, and overriden per zone.