Fix mesh level serialization

Fixed mesh level serialization

src/Tools/babylon.sceneSerializer.ts

@@ -120,6 +120,11 @@
             serializationObject.physicsImpostor = mesh.getPhysicsImpostor().type;
         }
 
+        // Metadata
+        if (mesh.metadata) {
+            serializationObject.metadata = mesh.metadata;
+        }
+
         // Instances
         serializationObject.instances = [];
         for (var index = 0; index < mesh.instances.length; index++) {