Added mesh 'metadata' serialization support

Must manually serialize metadata for meshes

src/Mesh/babylon.mesh.js

@@ -1541,6 +1541,9 @@ var BABYLON;
             mesh.id = parsedMesh.id;
             BABYLON.Tags.AddTagsTo(mesh, parsedMesh.tags);
             mesh.position = BABYLON.Vector3.FromArray(parsedMesh.position);
+            if (parsedMesh.metadata !== undefined) {
+                mesh.metadata = parsedMesh.metadata;
+            }
             if (parsedMesh.rotationQuaternion) {
                 mesh.rotationQuaternion = BABYLON.Quaternion.FromArray(parsedMesh.rotationQuaternion);
             }

src/Mesh/babylon.mesh.ts

@@ -1741,6 +1741,10 @@
 
             mesh.position = Vector3.FromArray(parsedMesh.position);
 
+            if (parsedMesh.metadata !== undefined) {
+                mesh.metadata = parsedMesh.metadata;
+            }
+
             if (parsedMesh.rotationQuaternion) {
                 mesh.rotationQuaternion = Quaternion.FromArray(parsedMesh.rotationQuaternion);
             } else if (parsedMesh.rotation) {