Fixing stacks and 2D histograms in the plotter #55
Description
The stacked 2D histograms are relatively useless in the plotter. This commonly comes up when wanting to compare, e.g., data to a sum of signal + background in some 2D plane. The problem is that the plotter draws the signal + background a s 2D stack which is not helpful. It would be better to create a single 2D histogram that is the sum and draw it instead. This requires a little reworking of the PlotFactory class.