add semester selection to seminar dates, fixes #3633

git-svn-id: svn://develop.studip.de/studip/trunk@27147 c5b85792-5220-0410-ad23-ed5b6b8ad999
fix multiple rendering re #3632

git-svn-id: svn://develop.studip.de/studip/trunk@27148 c5b85792-5220-0410-ad23-ed5b6b8ad999