Add legacy migration test app

test/LegacyTestApp/SquirrelLogger.cs

@@ -0,0 +1,27 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace LegacyTestApp
+{
+    internal class SquirrelLogger : Squirrel.SimpleSplat.ILogger
+    {
+        protected SquirrelLogger()
+        {
+        }
+
+        public Squirrel.SimpleSplat.LogLevel Level { get; set; }
+
+        public static void Register()
+        {
+            Squirrel.SimpleSplat.SquirrelLocator.CurrentMutable.Register(() => new SquirrelLogger(), typeof(Squirrel.SimpleSplat.ILogger));
+        }
+
+        public void Write(string message, Squirrel.SimpleSplat.LogLevel logLevel)
+        {
+            Console.WriteLine(message);
+        }
+    }
+}