Fix: Adding a node to a graph container adds it to the graph instead

When the constructors in the GraphNode class have been unified, we
wrongfully pass "graphModel.getGraph()" as an argument instead of the
current container. This causes all nodes to be added to the parent
graph.

See the UML example for reference. One of the class diagrams should be
contained by the UML container, but all three are part of the parent
graph instead.

Amends a13541f

org.eclipse.zest.core/src/org/eclipse/zest/core/widgets/GraphNode.java

@@ -101,15 +101,15 @@ public GraphNode(IContainer graphModel, int style) {
 	}
 
 	public GraphNode(IContainer graphModel, int style, Object data) {
-		this(graphModel.getGraph(), style, "" /* text */, null /* image */, data);
+		this(graphModel, style, "" /* text */, null /* image */, data);
 	}
 
 	public GraphNode(IContainer graphModel, int style, String text) {
 		this(graphModel, style, text, null);
 	}
 
 	public GraphNode(IContainer graphModel, int style, String text, Object data) {
-		this(graphModel.getGraph(), style, text, null /* image */, data);
+		this(graphModel, style, text, null /* image */, data);
 	}
 
 	public GraphNode(IContainer graphModel, int style, String text, Image image) {