[FEATURE] Smart-Content performance (loading with content query)

__Tasks:__

- [x] test coverage
- [ ] gather feedback for my changes

__New Issues:__
* https://github.com/sulu-cmf/sulu-standard/issues/278

__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | no => https://github.com/sulu-cmf/sulu/pull/263
| Fixed tickets | https://github.com/sulu-cmf/sulu-standard/issues/200
| BC Breaks     | yes => TODO
| Doc           | TODO
`strtolower($this->config['sortMethod'])`