1.3.1 Can chart sums e.g. line chart of total income per month by product

Written for SOFA Statistics by Grant Paton-Simpson on 2013-01-10

Adding sum as an option for charting e.g. a line chart showing total income per month by product.
Matplotlib scatterplots now have optimal min and max settings calculated for their x-axis.
Added footnote to Wilcoxon output explaining that different statistics packages may report the test statistic differently.
Misc fixes to chart layout including left margin offset.
Easier to add new variable definition files from within dialog for choosing them.
Modified recode column labels and help content to reduce confusion about which columns to enter range information into.