Vizlib Combo Chart - Grid formatting

Hi!

I think it would be good to have the same grid formatting options in the combo chart object as we have available in the line chart/bar chart objects.

This would allow us to have a common theme among our charts, when we have both line charts & combo charts on the same sheet.

At the moment we can set horizontal grid lines and coloured, striped background formatting on line charts, but these options are not available on the combo chart feature.