added a demo for rangebar brush

[davidchateau]

New Pull Request

This is a demo for the brush function with rangebars, after fix #4071
I hope it's nice and clear

Type of change

just a new demo file: new xml file, + the 3 html files that were generated automatically

Checklist:

• [x ] My code follows the style guidelines of this project
• [x ] I have performed a self-review of my own code
• [x ] I have commented my code, particularly in hard-to-understand areas
• [x ] My changes generate no new warnings
• [x ] I have added tests that prove my fix is effective or that my feature works
• [x ] New and existing unit tests pass locally with my changes