cronjobs: allow tasks to be executed independently, re #4003

git-svn-id: svn://develop.studip.de/studip/trunk@29970 c5b85792-5220-0410-ad23-ed5b6b8ad999
js: use new helper functions in cronjobs admin area, re #4308

git-svn-id: svn://develop.studip.de/studip/trunk@29971 c5b85792-5220-0410-ad23-ed5b6b8ad999