added missing datepicker for banner, re #3462

git-svn-id: svn://develop.studip.de/studip/trunk@29346 c5b85792-5220-0410-ad23-ed5b6b8ad999
prevent xss re #4178

git-svn-id: svn://develop.studip.de/studip/trunk@29347 c5b85792-5220-0410-ad23-ed5b6b8ad999