increase configuration service robustness by providing default object

This change is intended to:
* clean up the code by removing the necessity to check wether the value is provided by the backend.
* increase robustness by having a default to fall back.
@ulferts For Object/Collection operations/iteration, I'd prefer to stick to Lo-Dash. [_.merge](https://lodash.com/docs#merge) is probably what you're looking for. If we didn't have nested settings, [_.defaults](https://lodash.com/docs#defaults) would be perfect.