Change note publication logs

Allow change notes to be stored in the publication logs for export at publish time. 

This is an extension of the work carried out to export change notes to make them available on the front end.
As for the publication_logger. We only use this to create log entries for user based publication as far as I understand. If we introduce it to the republication (i.e. script based republishing) we would create PublicationLog entries for each script based publish. This would also appear on the front end as change notes unless we change how change notes are exported. Perhaps this is something we SHOULD have in the republication but I'm not sure if it should appear as change notes. The PublicationLog requires a change note. Im currently looking into what should happen if the update is minor. We shouldn't create a PublicationLog entry come to think of it if it is minor (I think) and it would fail validation if we tried. Im not currently sure how that part works!