Discussions

- Implemented discussion library widget
- Implemented create discussion widget
- Implemented discussion profile
- Added discussions to search
- Fixed contentcomments to work with new API and renamed to comments
- Added discussions to activity widget
- Created discussions and comments API
- Renamed permissions options in clips to 'Manage access'
- Various docs fixes
- Fixed timeago to work with new timestamps

This PR builds on top of #2803 and requires the `messagebox` PR from Hilary.