The addChildren gets promoted to being a method of the Uize.Widget base class. This method shouldl be used in place of the addChildButton method in the Uize.Widget.Button class, as well as in other places where it is convenient.
The Uize.Widget.Button class gets a simple action state property for convenience in simple cases where you just want to instantiate a button widget that has a click action.
Pass the DOM event as an argument to the action function
Updated some widgets to use the addChildren method in place of the ugly old addChildButton technique.