[WIP] BDD: add content type group create/read to REST

To do:
- [x] change feature file to use an actual rest client
- [x] change feature file to use ValueObjectHelper (need ezpublish-community#136)
- [x] remove object mapping (at least for now since there is no need for content type groups)
- [x] Implement Authentication sentences
- [x] Implement Error sentences
- [x] Implement ContentTypeGroup sentences
- [ ] waiting for  ezpublish-community#136 to be merged