OWPaintData: PEP 8 (except for connecting signals)
OWPaintData: changed signal connections to the new style
Added Dlg_enter icon for line edits and similar controls with callback
OWPaintData: attr names can now be changed and are added to settings
OWPaintData: added main (for testing)
OWWidget.__new__'s argument parent now has a default value (None)
OWPaintData: added color labels to list view with class names, removed legend from the plot
OWPaintData: rearranged the toolbox, simplified the radius and density, added icons for undo, redo, clear