Added (the mysteriously disappearing) icon for BoxPlot
Modified stored procedures for discretization. Modified to_sql() in DiscreteVariable.
Pass domain as parameter to find_or_create_context.
Added basic heatmap widget
Merge branch 'master' into heatmap, to update boxplot.
Merge branch 'master' into heatmap
Added fixed (with given min and max) EqualWidth discretization. Needed
by Heatmap widget.
Modified Heatmap widget.
Modified Heatmap widget. Added progress bar.