[WIP] RangeSlider

- [x] Base class is now __Slider__
- [x] Changed __RangeStart__ to __Minimum__
- [x] Changed __RangeStop__ to __Maximum__
- [x] __Minimum__ cannot be set greather than __RangeSliderStart__ and vice versa (Fixes #837)
- [x] __Maximum__ cannot be set smaller than __RangeSliderStop__ and vice versa (Fixes #837)
- [ ] The difference between __Minimum__ and __Maximum__ cannot be smaller than __MinRange__
- [ ] Add property to show/hide Ticks
- [ ] Fix incorrect handling of Start/Stop. Left thumb is moving incorrect (Fixes #872)
- [ ] Improve Range Slider events (Fixes #856)

Suggestions by @QuantumDeveloper:


- [x] Rename RangeStartSelected/StopSelected to LowerValue/UpperValue (I think It will more clearer)
- [x] Add event handler for each of both events
- [ ] Add event handler for lower and upper Thumbs like Drag started, drag completed (4 events together)
- [ ] Add support of vertical orientation
- [ ] Remove annoying issue when left thumb push central and right thumb to the rigth‏
- [ ] Fix issue wih incorrect width calculation‏
- [ ] MoveToPoint (if I click then the thumb moves to that point)
- [ ] small/large change if MoveToPoint not enabled  
- [ ] support of preview/mouse events on repeat buttons

Memo for me:
- [ ] TumbWidth shoulb be {DynamicResource HorizontalThumbWidth}
- [ ] Track should not be hardcoded

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FIXES #885