Create custom node icon on startPage

Issue: http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-3868
@Benglin Please help me to review it. Thanks
Wrong place, it should be inside ```if (args.Success)```, that's the whole idea of putting it here, if user chooses not to proceed with creating a custom node. Putting it here makes no difference at all.