normalized converters code

src/Shared/HandyControl_Shared/Tools/Converter/Object2StringConverter.cs

@@ -10,7 +10,7 @@ namespace HandyControl.Tools.Converter
 
         public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
         {
-            throw new NotImplementedException();
+            throw new NotSupportedException();
         }
     }
 }