dialogs: rename default close button to 'close', use name from embedded .cancel button in response if available, re #4404

git-svn-id: svn://develop.studip.de/studip/trunk@30940 c5b85792-5220-0410-ad23-ed5b6b8ad999
helpbar: fix interpolating of string and fallback to german helpbar texts if no other are available, re #3768, fixes #4472

git-svn-id: svn://develop.studip.de/studip/trunk@30941 c5b85792-5220-0410-ad23-ed5b6b8ad999