feat: Added link to JFX-Central in menu Help/JavaFX/<JFX-Central>.

[Oliver-Loeffler]

Issue

Fixes #569 Relates to discussion #484

Progress

• [x] Change must not contain extraneous whitespace
• [x] License header year is updated, if required
• [x] The PR name must follow the pre-defined format
• [x] Verify the contributor has signed Gluon Individual Contributor License Agreement (CLA)