Add project files.

ObservatoryCore/ObservatoryCore.cs

@@ -0,0 +1,23 @@
+using System;
+using Avalonia;
+using Avalonia.ReactiveUI;
+
+namespace Observatory
+{
+    class ObservatoryCore
+    {
+        [STAThread]
+        static void Main(string[] args)
+        {
+            BuildAvaloniaApp().StartWithClassicDesktopLifetime(args);
+        }
+
+        public static AppBuilder BuildAvaloniaApp()
+        {
+            return AppBuilder.Configure<UI.MainApplication>()
+                .UsePlatformDetect()
+                .LogToTrace()
+                .UseReactiveUI();
+        }
+    }
+}