Converge downstream reading_info feature with upstream
Port downstream only idiom to update reading_info table Make more use of api when retrieving forum and message information Optimize message existance query
- remove hardcoded dependency with registered_users group. Target is to improve suitability in convoluted multi groups/multi subsites context - in place of previous permission-based machinery, use plain table columns to detect whether user can or cannot post replies/new threads - remove permission check at the message level in favor of that on forum level