Folders

This PR brings in further integration for OAE in the following aspects:
 - Activities
 - Search
 - Previews
 - REST Docs
 - Extra functionality such as updating, deleting, ..
We can probably do something similar to the content API:

```
FoldersAPI.emit(FoldersConstants.events.UPDATED_FOLDER, ctx, folder, updatedFolder);

// Get the full folder profile for the updated folder
return _getFullFolderProfile(ctx, updatedFolder, callback);
```