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'm not a huge fan of this coding style. I find something like this easier to read:

```
// We're only interested in the groups
var groups = _.filter(principals, function(principal) {
    return AuthzUtil.isGroupId(principal.id);
});
return _.map(groups, function(authzGroup) {
  // Return a light-weight folder
  return {'groupId': authzGroup.id};
});
```