refine and reposition 'mark all as read', closes #2421

git-svn-id: svn://develop.studip.de/studip/trunk@25202 c5b85792-5220-0410-ad23-ed5b6b8ad999
reposition 'mark all as read' again, refines [25202], re #2421

git-svn-id: svn://develop.studip.de/studip/trunk@25203 c5b85792-5220-0410-ad23-ed5b6b8ad999