refs #3218: change icon on change of context

git-svn-id: svn://develop.studip.de/studip/trunk@25665 c5b85792-5220-0410-ad23-ed5b6b8ad999
refs #2878 : alert only for unseen notifications

git-svn-id: svn://develop.studip.de/studip/trunk@25666 c5b85792-5220-0410-ad23-ed5b6b8ad999