Fix issues with StarRating
add missing ProgressBar tests
remove unused code
fix Widget-attr test to correspond to changes in ce4acef67372b9ba570f7e93e62b35f4654f907d
rename _WidgetBase --> Widget
rename _Contained --> Contained, _Container --> Container
rename _CssStateMixin --> CssState
rename _HasDropDown --> HasDropDown
rename _BidiMixin --> Bidi
rename _KeyNavMixin --> KeyNav
Rename _FormWidgetMixin --> FormWidget, _FormValueMixin --> FormValueWidget.
Also remove form/_FormWidget and form/_FormValueWidget.
rename _Invalidating --> Invalidating
Remove _FocusMixin.
It's not really needed now that I moved onFocus() onBlur() etc. into Widget.