remove old infobox and migrate to global-layout, re #4620

git-svn-id: svn://develop.studip.de/studip/trunk@31455 c5b85792-5220-0410-ad23-ed5b6b8ad999
re#3768

add preview to message composer

git-svn-id: svn://develop.studip.de/studip/trunk@31456 c5b85792-5220-0410-ad23-ed5b6b8ad999