UI::CheckBox: add Toggle, SetState, IsChecked, onValueChanged (and Lua API)
UI::List: Add {Get,Set}SelectedIndex, NumItems, IsEmpty (and Lua API)
UI::TextEntry: add Lua binding for SetText
UI::Slider: add {Get,Set}Range and fill in Lua API
UI::DropDown: expose the same {Get,Set}SelectedIndex API as UI::List