Folders

This PR brings in further integration for OAE in the following aspects:
 - Activities
 - Search
 - Previews
 - REST Docs
 - Extra functionality such as updating, deleting, ..
Unfortunately that's not possible as it depends on what streams is being authorized. For example, authorizing a scribe request to a user's activity stream doesn't require a signature as we can simply check if the current user equals the owner of the activity stream.