plotutil.AddBarCharts

Original [issue 96](https://code.google.com/p/plotinum/issues/detail?id=96) created by eaburns on 2012-11-05T14:00:15.000Z:

Should make a plotutil function for adding bar charts. It should also allow one to add grouped bar charts. This may be possible by allowing not only a string parameter to name a bar chart, but also by allowing an int parameter to precede the data which specifies its offset.