Add feature to print group summary

[me21]

Please add feature to print group summary rows.

[abenhamdine]

I will give a try when i have some time but I can't promise anything ;)
Side note : corresponding issue in loiane repo : loiane#11

[me21]

Thank you, I'll wait. I've seen that issue in loiane, but I'm only starting to learn Ext JS, so I don't have enough experience to fix it myself.
The commits in loiane since you've forked that repo don't seem to do smth. with group summary printing.