[ticket/12052] Add support for ITEM_UNAPPROVED to set_post_visibility method

PHPBB3-12052
[ticket/12052] Use a different visibility when a post was edited and needs to be reapproved

PHPBB3-12052
[ticket/11772] Do not send out new topic/post notifications when reapproving

Only add notifications, if we are not reapproving post
When the topic was already approved, but was edited and
now needs re-approval, we don't want to notify the users again.

PHPBB3-11772