Make initial velocity influence newtornian particles

[riccardobl]

I've changed the newtonian influence to not ignore the initial velocity since it is a default property.
I need a second opinion on whether this is a good idea or now, but it might help making it more versatile.

[github-actions]

🖼️ Screenshot tests have failed.

The purpose of these tests is to ensure that changes introduced in this PR don't break visual features. They are visual unit tests.

📄 Where to find the report:

• Go to the (failed run) > Summary > Artifacts > screenshot-test-report
• Download the zip and open jme3-screenshot-tests/build/reports/ScreenshotDiffReport.html

⚠️ If you didn't expect to change anything visual:
Fix your changes so the screenshot tests pass.

✅ If you did mean to change things:
Review the replacement images in jme3-screenshot-tests/build/changed-images to make sure they really are improvements and then replace and commit the replacement images at jme3-screenshot-tests/src/test/resources.

✨ If you are creating entirely new tests:
Find the new images in jme3-screenshot-tests/build/changed-images and commit the new images at jme3-screenshot-tests/src/test/resources.

Note; it is very important that the committed reference images are created on the build pipeline, locally created images are not reliable. Similarly tests will fail locally but you can look at the report to check they are "visually similar".

See https://github.com/jMonkeyEngine/jmonkeyengine/blob/master/jme3-screenshot-tests/README.md for more information

[yaRnMcDonuts]

I need a second opinion on whether this is a good idea or now,

As long as initial velocity is 0,0,0 by default, then this shouldn't break anything and sounds like a good idea.

[richardTingle]

This change seems reasonable.

I think the screenshot pipeline failed (rather than the tests themselves). Worth just rerunning them and they may pass (not sure if the github UI allows that. Pushing an empty commit would do it)