Move example fn widgets into sky/framework/components

sky/examples/fn/widgets/radio.dart

-part of widgets;
-
-class Radio extends ButtonBase {
-
-  Object value;
-  Object groupValue;
-  ValueChanged onChanged;
-
-  static Style _style = new Style('''
-    transform: translateX(0);
-    display: inline-block;
-    -webkit-user-select: none;
-    width: 14px;
-    height: 14px;
-    border-radius: 7px;
-    border: 1px solid blue;
-    margin: 0 5px;'''
-  );
-
-  static Style _highlightStyle = new Style('''
-    transform: translateX(0);
-    display: inline-block;
-    -webkit-user-select: none;
-    width: 14px;
-    height: 14px;
-    border-radius: 7px;
-    border: 1px solid blue;
-    margin: 0 5px;
-    background-color: orange;'''
-  );
-
-  static Style _dotStyle = new Style('''
-    -webkit-user-select: none;
-    width: 10px;
-    height: 10px;
-    border-radius: 5px;
-    background-color: black;
-    margin: 2px;'''
-  );
-
-  Radio({
-    Object key,
-    this.onChanged,
-    this.value,
-    this.groupValue
-  }) : super(key: key);
-
-  Node build() {
-    return new Container(
-      style: _highlight ? _highlightStyle : _style,
-      children: value == groupValue ?
-          [super.build(), new Container( style : _dotStyle )] : [super.build()]
-    )..events.listen('click', _handleClick);
-  }
-
-  void _handleClick(_) {
-    onChanged(value);
-  }
-}