events: trigger 'review_status_change' when reviewers are updated.
- small code refactoring
- extended commenting event with comment
- extended review_status_change event with new status
permissions: handle more cases for invalidating permission caches
- invalidate user permissions on chaning the global permissions
- invalidate all users in case of creating new object with "copy permissions" flag
- invalidate all users permissions in case of repo/repo group renames
- invalidate all user permissions in forked repo with copy flag