[API Review] Make Scene styleable through CSS

[David Grieve]

https://javafx-jira.kenai.com/browse/RT-31282

Scene has a fillProperty which should be styleable via CSS but this would 
require making Scene implement the javafx.css.Styleable interface. The 
interesting bits from the interface are 

    public String getId() 
    public ObservableList<String> getStyleClass() 
    public String getStyle() 
    public ObservableSet<PseudoClass> getPseudoClassStates() 

Scene will have a "scene" style-class by default. 

getId() and getStyle() will be backed by corresponding properties with setters. 

    public void setId(String newId) 
    public final StringProperty idProperty() 
    public void setStyle(String style) 
    public final StringProperty styleProperty() 

There is no setPseudoClassStates method since pseudo-class states are handled 
internally. The only pseudo-class state for Scene is :dir which corresponds to 
node orientation. 

public String getTypeSelector() will return "Scene". 

The following CSS properties will be supported for Scene: 

    -fx-cursor: <cursor | url>; 
    -fx-fill: <paint>;