smartGWT: Support Grouping by more than one column

[fatzopilot]

Seems to be possible in smartClient but I could be wrong.

[sjivan]

It is supported in Smart GWT as well. See ListGrid.groupBy(String[] fields).

Sanjiv

[fatzopilot]

Thanks for adding this. Would be even nicer if the user was able to do the grouping. I.e. instead of resetting the current group state when the user selects another field to group by, just add that group.