Folders

This PR brings in further integration for OAE in the following aspects:
 - Activities
 - Search
 - Previews
 - REST Docs
 - Extra functionality such as updating, deleting, ..
I think we should have a more detailed `updateFolderContentVisibility` test that validates the different permutations (e.g. content that can be updated, content that cannot be updated for various reasons, etc.)