Add wheelPropagationDisabledIfScrollable option

[SvenSchoene]

• Read CONTRIBUTING.md
• Run npm test to make sure it formats and build successfully
• Provide the scenario this PR will address(some JSFiddles will be perfect)
  • I describe the use-case for this below.
• Refer to concerning issues if exist
  • No existing issues regarding this found.

We have a specific use case regarding wheel propagation: When there is a container with a scroll bar, we want wheelPropagation: false. However, when the container does not have a scroll bar, we want wheelPropagation: true.

This was not really possible to implement outside of this library.

I added three new examples for this.

Example code:

const ps = new PerfectScrollbar(demo, {
  wheelPropagationDisabledIfScrollable: true,
});

I read the contributions guide; ran the formatter; re-built the source files so that /dist is updated; updated the typescript file; and added an example.