Added Avalonia sample application

SampleApps/AvaloniaApp/Program.cs

@@ -0,0 +1,24 @@
+using Avalonia;
+using System;
+
+namespace AvaloniaApp
+{
+    class Program
+    {
+        [STAThread]
+        public static void Main(string[] args)
+        {
+            BuildAvaloniaApp()
+                .StartWithClassicDesktopLifetime(args);
+        }
+
+        public static AppBuilder BuildAvaloniaApp()
+        {
+            return AppBuilder
+                .Configure<App>()
+                .UsePlatformDetect()
+                .WithInterFont()
+                .LogToTrace();
+        }
+    }
+}