Folders

This PR brings in further integration for OAE in the following aspects:
 - Activities
 - Search
 - Previews
 - REST Docs
 - Extra functionality such as updating, deleting, ..
This is an issue with the activity aggregator / rules surrounding sharing. These issues are present in content and discussion as well. This feels like something that can be tackled as part of a separate issue so I've ticketed it at https://github.com/oaeproject/Hilary/issues/1028