RangeSlider - Missing RangeSlider style in Java11 version

[dukke]

Before importing the style definitions on master branch (Java 8 version), we need to do a PR in ControlsFX, which is where the RangeSlider control comes from. That PR's purpose would be to fix the RangeSlider skin which doesn't support non round thumbs. The master branch has a version of the RangeSliderSkin that allows non round thumbs.