Shortcut for Sphere brush

Instead of creating a new widget, refer to the Segment Editor module’s widget:

segmentEditorWidget = slicer.modules.segmenteditor.widgetRepresentation().self().editor
paintEffect = segmentEditorWidget.effectByName("Paint")
paintEffect.setCommonParameter("BrushSphere", 1)  # enable
paintEffect.setCommonParameter("BrushSphere", 0)  # disable