Added resource classses and a missing converter.

Harmonia.WinUI/Converters/DoubleToPercentConverter.cs

@@ -0,0 +1,25 @@
+using Microsoft.UI.Xaml.Data;
+using System;
+
+namespace Harmonia.WinUI.Converters;
+
+public sealed partial class DoubleToPercentConverter : IValueConverter
+{
+    public DoubleToPercentConverter()
+    {
+
+    }
+
+    public object? Convert(object value, Type targetType, object parameter, string language)
+    {
+        if (value is not double doubleValue)
+            return null;
+
+        return Math.Round(doubleValue * 100) + "%";
+    }
+
+    public object ConvertBack(object value, Type targetType, object parameter, string language)
+    {
+        throw new NotImplementedException();
+    }
+}