Added main menu

MainWindowViewModel.cs

@@ -0,0 +1,49 @@
+using Avalonia;
+using Avalonia.Media.Imaging;
+using ReactiveUI;
+using System;
+using System.Reactive;
+using Path = System.IO.Path;
+
+namespace AvaloniaCoreRTDemo
+{
+    public class MainWindowViewModel: ReactiveObject
+    {
+        public MainWindowViewModel()
+        {
+            DotNetImage = new Bitmap(Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "dotnet.png"));
+            AvaloniaImage = new Bitmap(Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "avalonia.png"));
+
+            FileExitCommand = ReactiveCommand.Create(RunFileExit);
+            HelpAboutCommand = ReactiveCommand.Create(RunHelpAbout);
+        }
+        
+        public IBitmap DotNetImage
+        {
+            get { return dotNetImage; }
+            set { this.RaiseAndSetIfChanged(ref this.dotNetImage, value); }
+        }
+
+        public IBitmap AvaloniaImage
+        {
+            get { return avaloniaImage; }
+            set { this.RaiseAndSetIfChanged(ref this.avaloniaImage, value); }
+        }
+
+        public ReactiveCommand<Unit, Unit> FileExitCommand { get; }
+        public ReactiveCommand<Unit, Unit> HelpAboutCommand { get; }
+
+        void RunFileExit()
+        {
+            Environment.Exit(0);
+        }
+
+        void RunHelpAbout()
+        {
+            // Code for executing the command here.
+        }
+
+        private IBitmap dotNetImage;
+        private IBitmap avaloniaImage;
+    }
+}