Add scale property on the `MouseRangeManipulator` to control its speed

### Problem

The scroll can be too slow with `MouseRangeManipulator` (ex: slicing)

### Suggested solution 

Add a `scale` property on the listener objects of the `MouseRangeManipulator` to be consumed in `processDelta` to control the rate of change. Keeping the `scale` optional/defaulting to `1` should make it backward compatible.
