BREAKING CHANGE: replaced universe objects with root universe object

Engine.Core/Extensions/UniverseObjectExtensions.cs

@@ -16,6 +16,21 @@ public static class UniverseObjectExtensions
         return universeObject;
     }
 
+    public static IEnumerator<IUniverseObject> TraverseChildren(this IUniverseObject universeObject)
+    {
+        static IEnumerable<IUniverseObject> Traverse(IUniverseObject obj)
+        {
+            foreach (IUniverseObject child in obj.Children)
+            {
+                yield return child;
+                foreach (IUniverseObject descendant in Traverse(child))
+                    yield return descendant;
+            }
+        }
+
+        return Traverse(universeObject).GetEnumerator();
+    }
+
     #region Universe Object Search
     /// <summary>
     /// Gets a <see cref="IUniverseObject"/> of the specified type.