fix: Scene Builder now shows a message which FXML imports were not resolvable

[Oliver-Loeffler]

Issue

Up to now, Scene Builder did not load FXML files with unresolvable imports. This is basically enabled by PR #576. This PR enables Scene Builder to provide a list of failing imports to the user, together with an instruction on how to include the missing classes/JAR files in Scene Builder.

The EditorDialog in com.oracle.javafx.scenebuilder.kit.editor.panel.util.dialog has been updated so that its Detail window has also the correct application icon and window title. The main EditorDialog also now has the correct application icon.

Fixes #281 but requires PR #576 first

Progress

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