Convert the Swing Dialog to JavaFX

[Super-Tang]

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• Change in CHANGELOG.md described
• Tests created for changes
• Manually tested changed features in running JabRef
• Screenshots added in PR description (for bigger UI changes)
• Ensured that the git commit message is a good one
• Check documentation status (Issue created for outdated help page at help.jabref.org?)

[Super-Tang]

We convert part of the swing dialog to javafx. The dialog we are trying to change is Options->Preferences.

[tobiasdiez]

Oh wow, with the preferences you actually took the most complex of all dialogs ;-). From what I can see, you already made good progress. Nice!
I would suggest you try to merge with the current master so that some of the code changes in master are no longer shown as differences and then I'll have a look and give you feedback.

[Siedlerchr]

In addition to what Tobias says, in future please create a new branch for a feature or issue to work on and to commit to. This make it easier for you and us to review the changes.

[tobiasdiez]

What's the relation of this PR with #4253?

[Super-Tang]

They are the same. I just created a new branch, and pushed my changes to the branch. I will close this PR at once. @tobiasdiez