Change ExName to Attached Property

It is more powerfull and better then inherence and we can use colour emojies easier.

v2rayN/v2rayN/Base/MyDGTextColumn.cs

@@ -1,9 +0,0 @@
-using System.Windows.Controls;
-
-namespace v2rayN.Base
-{
-    internal class MyDGTextColumn : DataGridTextColumn
-    {
-        public string ExName { get; set; }
-    }
-}

v2rayN/v2rayN/Base/MyDgTextColumnAttachedProperties.cs

@@ -0,0 +1,20 @@
+using System.Windows;
+
+namespace v2rayN.Base
+{
+	public static class MyDgTextColumnAttachedProperties
+	{
+		public static readonly DependencyProperty ExNameProperty =
+			DependencyProperty.RegisterAttached("ExName", typeof(string), typeof(MyDgTextColumnAttachedProperties), new PropertyMetadata(default(string)));
+
+		public static void SetExName(DependencyObject element, string value)
+		{
+			element.SetValue(ExNameProperty, value);
+		}
+
+		public static string GetExName(DependencyObject element)
+		{
+			return (string)element.GetValue(ExNameProperty);
+		}
+	}
+}