Send Change History to Content API

With the change notes, we were only persisting the latest change note. This commit inserts a hash of the timestamp and change note into a change history Array and sends this to the content API.

It also deals with minor update checkbox and major update change note persistence between versions.
can we extract method this action to keep the `#publish` method clean? `append_change_history unless document.minor_update` I think would read better here.