Forum:
- fix online-status
- change wording of permission-denoting text for users
- add a grace time of 5 minutes before marking a posting as "edited"
- fall back to seminar_id if an invalid topic_id is submitted


git-svn-id: svn://develop.studip.de/studip/trunk@25512 c5b85792-5220-0410-ad23-ed5b6b8ad999