Add support for inheritance of dialogs

[koppor]

You all know, I like inheritance instead of swich/case or ifs. Therefore, I crafted following code for the super class:

        ViewLoader.view(ExtractBibtexDialog.class)
                  .controller(this)
                  .load()
                  .setAsDialogPane(this);

classDiagram
    ExtractBibtexDialog <|-- ExtractBibtexDialogGrobid
    ExtractBibtexDialog <|-- ExtractBibtexDialogOffline

Loading

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I could solve it differently. Leaving this PR for future reference

[koppor]

Sorry, even with more cleaner code, it doesn't work without that patch.

[koppor]

@calixtus Required by JabRef/jabref#11565. I hope, I find time to propose another solution using some composition or helper class instead of one-level inheritance.

[koppor]

Not required. We went for if then else