add remaining documentation, refs #4119

git-svn-id: svn://develop.studip.de/studip/trunk@29583 c5b85792-5220-0410-ad23-ed5b6b8ad999
re #3985
descriptional text for modules only present in AdminModules and not as own class

git-svn-id: svn://develop.studip.de/studip/trunk@29584 c5b85792-5220-0410-ad23-ed5b6b8ad999