sidebar: remove special infobox styling (in order to reduce confusion in release), re #3768

git-svn-id: svn://develop.studip.de/studip/trunk@31439 c5b85792-5220-0410-ad23-ed5b6b8ad999
sidebar: add default sidebar image, re #3768

git-svn-id: svn://develop.studip.de/studip/trunk@31440 c5b85792-5220-0410-ad23-ed5b6b8ad999
sidebar: infobox widgets should move back to top so they don't get lost, re #3768

git-svn-id: svn://develop.studip.de/studip/trunk@31441 c5b85792-5220-0410-ad23-ed5b6b8ad999