Folders

This PR brings in further integration for OAE in the following aspects:
 - Activities
 - Search
 - Previews
 - REST Docs
 - Extra functionality such as updating, deleting, ..
Not a huge fan of this code style. Would prefer something like this

```
// Remove null content items. This can happen if an item was deleted from
// the system but hasn't been removed from the libraries
contentItems = _.compact(contentItems);
// Augment each content item with its signed preview urls
_.each(contentItems, function(contentItem) {
  ContentUtil.augmentContent(ctx, contentItem);
});
```