You saved my day. Thank you, it is working. The minor bugs that i found so far:
1)When grouping field is selected via column context menu. Multi grouping disables.
2)Instead of showing sub grouping field in its column position, it can be removed completely.
I dont know if you continue to develop the code. But please dont forget to share if you improve it. I will try to add some functionality. I will share it if i can success.