Completely disable MouseWheelDirective if not needed

[novarx]

This makes it possible to still listen to onMouseWheel Events when no Zoom/Trackpad is enabled.

What kind of change does this PR introduce?

• [X] Bugfix
• [X] Feature
• [ ] Code style update (formatting, local variables)
• [ ] Refactoring (no functional changes, no api changes)
• [ ] Build related changes
• [ ] CI related changes
• [ ] Other... Please describe:

What is the current behavior?

It's currently not possible to listen to any mouseWheel Event, when hovering over the graph area, which i.e. prevents the page from scrolling. his behavior is because of MouseWheelDirective::mouseWheelFunc resp. event.preventDefault() which is always called, no matter if it is used or not.

What is the new behavior?

This Change makes it possible to still listen to onMouseWheel Events, if Zoom and Trackpad is disabled, over the graph.

Does this PR introduce a breaking change?

• [ ] Yes
• [x] No

[novarx]

If you need an working example, let me know.

[novarx]

@marjan-georgiev Any chance to get a review on that?