add ButtonGroup

replaced RadioButton with ButtonGroup

src/Shared/HandyControlDemo_Shared/UserControl/Controls/ButtonGroupDemoCtl.xaml.cs

@@ -0,0 +1,40 @@
+using System.Windows;
+using System.Windows.Media.Imaging;
+
+namespace HandyControlDemo.UserControl
+{
+    public partial class ButtonGroupDemoCtl
+    {
+        public ButtonGroupDemoCtl()
+        {
+            InitializeComponent();
+        }
+
+        public static readonly DependencyProperty SourceProperty = DependencyProperty.Register(
+            "Source", typeof(BitmapFrame), typeof(Avatar), new PropertyMetadata(default(BitmapFrame)));
+
+        public BitmapFrame Source
+        {
+            get => (BitmapFrame) GetValue(SourceProperty);
+            set => SetValue(SourceProperty, value);
+        }
+
+        public static readonly DependencyProperty UserNameProperty = DependencyProperty.Register(
+            "DisplayName", typeof(string), typeof(Avatar), new PropertyMetadata(default(string)));
+
+        public string DisplayName
+        {
+            get => (string) GetValue(UserNameProperty);
+            set => SetValue(UserNameProperty, value);
+        }
+
+        public static readonly DependencyProperty LinkProperty = DependencyProperty.Register(
+            "Link", typeof(string), typeof(Avatar), new PropertyMetadata(default(string)));
+
+        public string Link
+        {
+            get => (string) GetValue(LinkProperty);
+            set => SetValue(LinkProperty, value);
+        }
+    }
+}