Make BVH node fields final

CityDoctorParent/CityDoctorModel/src/main/java/de/hft/stuttgart/citydoctor2/datastructure/bht/Node.java

@@ -5,9 +5,9 @@ import java.util.List;
 
 public class Node<E> {
 	
-    private List<Node<E>> children = new ArrayList<>();
-    private AABB aabb;
-    private E element;
+    private final List<Node<E>> children = new ArrayList<>();
+    private final AABB aabb;
+    private final E element;
 
     public Node(E element, AABB aabb) {
     	this.aabb = aabb;