* The widget classes have been renamed from `*Widget` to `*`.  The old names are 
  still functional, but are deprecated.  i.e. `IntSliderWidget` has been renamed 
  to `IntSlider`.
* The ContainerWidget was renamed to Box and no longer defaults as a flexible
  box in the web browser.  A new FlexBox widget was added, which allows you to
  use the flexible box model.