Folders

This PR brings in further integration for OAE in the following aspects:
 - Activities
 - Search
 - Previews
 - REST Docs
 - Extra functionality such as updating, deleting, ..
When 2 folders are shared with 2 users, 8 activities are published to the activity stream: 

- Folder 1 has been shared with user A
- Folder 2 has been shared with user A
- Folder 1 has been shared with user B
- Folder 2 has been shared with user B
- Role of user A on Folder 1 has been updated
- Role of user B on Folder 1 has been updated
- Role of user A on Folder 2 has been updated
- Role of user B on Folder 2 has been updated

This should be cut down to ensure that a more comprehensive activity update is provided. The first 4 should be aggregated into something more intelligent. None of the role updates should be in the activity feed when a folder is shared.