App.init() must not use JavaFX controls / scene graph

See Javadoc for Application.init():

    /**
     * The application initialization method. This method is called immediately
     * after the Application class is loaded and constructed. An application may
     * override this method to perform initialization prior to the actual starting
     * of the application.
     *
     * <p>
     * The implementation of this method provided by the Application class does nothing.
     * </p>
     *
     * <p>
     * NOTE: This method is not called on the JavaFX Application Thread. An
     * application must not construct a Scene or a Stage in this
     * method.
     * An application may construct other JavaFX objects in this method.
     * </p>
     * @throws java.lang.Exception if something goes wrong
     */

Move all code that has anything to do with theUI into the start() method or something called from there.

Rihpsalis / GhostGame

App.init() must not use JavaFX controls / scene graph #6