normalized converters code

src/Shared/HandyControlDemo_Shared/Tools/Converter/HatchBrushConverter.cs

@@ -27,7 +27,7 @@ namespace HandyControlDemo.Tools.Converter
 
         public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
         {
-            throw new NotImplementedException();
+            throw new NotSupportedException();
         }
     }
 }

src/Shared/HandyControlDemo_Shared/Tools/Converter/String2BrushConverter.cs

@@ -15,7 +15,7 @@ namespace HandyControlDemo.Tools.Converter
 
         public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
         {
-            throw new NotImplementedException();
+            throw new NotSupportedException();
         }
     }
 }

src/Shared/HandyControlDemo_Shared/Tools/Converter/StringRepeatConverter.cs

@@ -39,7 +39,7 @@ namespace HandyControlDemo.Tools.Converter
 
         public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
         {
-            throw new NotImplementedException();
+            throw new NotSupportedException();
         }
     }
 }