normalize util.bound to Box3 extensions

src/mesh/model.js

@@ -103,6 +103,7 @@ mesh.model = class MeshModel extends mesh.object {
         meh.castShadow = true;
         meh.renderOrder = 1;
         // center vertices then restore mesh object position
+        // still this doesn't work. scale broken for bounding boxes
         // let mid = meh.getBoundingBox().mid;
         // geo.moveMesh(-mid.x, -mid.y, -mid.x);
         // this.move(mid.x, mid.y, mid.x);