mark DBMigration as deprecated, re #5170

git-svn-id: svn://develop.studip.de/studip/trunk@32814 c5b85792-5220-0410-ad23-ed5b6b8ad999
fix navigation for inst-admins, fixes #5180

git-svn-id: svn://develop.studip.de/studip/trunk@32815 c5b85792-5220-0410-ad23-ed5b6b8ad999