datepicker: add css class 'has-date-picker' that instantiates a datepicker on the according object, fixes #5126

git-svn-id: svn://develop.studip.de/studip/trunk@32912 c5b85792-5220-0410-ad23-ed5b6b8ad999
js: generic method for confirmations (this commit fixes a neglectable but still ugly shortcoming in data-proxyfor as well), fixes #5217

git-svn-id: svn://develop.studip.de/studip/trunk@32913 c5b85792-5220-0410-ad23-ed5b6b8ad999