re #2874
better documentation for controller and migration

git-svn-id: svn://develop.studip.de/studip/trunk@25526 c5b85792-5220-0410-ad23-ed5b6b8ad999
refs #3239, refactorize and fix migration, preventing recursion problems; create empty area on first visit of Forum (if no other area is present)

git-svn-id: svn://develop.studip.de/studip/trunk@25527 c5b85792-5220-0410-ad23-ed5b6b8ad999