Create getValue/getStep API methods

- [x] should get initial value on getValue()
- [x] should get value after drag and drop on getValue()
- [x] should get value set with setValue() on getValue()
- [x] should get closest step to initial value on getStep()
- [x] should get closest step after drag and drop on getStep()
- [x] should get closest step to value set with setValue() on getStep()
- [x] should get step set with setStep() on getStep()