feat: add icon for editor layout

BallanceTasEditor/Converters/NullableIntStringConverter.cs

@@ -1,19 +0,0 @@
-using System;
-using System.Collections.Generic;
-using System.Globalization;
-using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
-using System.Windows.Data;
-
-namespace BallanceTasEditor.Converters {
-    public class NullableIntStringConverter : IValueConverter {
-        public object Convert(object value, Type targetType, object parameter, CultureInfo culture) {
-            throw new NotImplementedException();
-        }
-
-        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) {
-            throw new NotImplementedException();
-        }
-    }
-}