Operate on selected histgrams

If two histograms (or more for Add) are selected one can perform the following operations: + Add: hist1 + factor*hist2 - Sub: hist1 - factor*hist2 * Mul: hist1 * factor*hist2 * Div: hist1 / (factor*hist2) The resulting histograms are shown and stored in memory with new names. Note that in this case the order of selection is important. If only 1 histogram is selected with operation multiply then this gets scaled For operation Add any number of selections are possible. Rebin a selected histogram using the selected (green) value. The new bin content may the sum or average of the original bins