Add 'message-undelete' page to make use of the new '::message::undelete' proc for undeleting messages, a couple of icons, the undelete option in 'message-list' and the undelete action in automated tests
Add 'lang::message::undelete', in order to provide an API for undeletion of messages deleted via 'lang::message::delete', and modify 'lang::message::edit' accordingly. Next step would be to provide a user interface for it.