feat: initialize, setup demo. make sure MVVM works.

demo/Ursa.Demo/DataTemplates/ViewLocator.cs

@@ -0,0 +1,29 @@
+using System;
+using Avalonia.Controls;
+using Avalonia.Controls.Templates;
+using Ursa.Demo.Pages;
+
+namespace Ursa.Demo.Converters;
+
+public class ViewLocator: IDataTemplate
+{
+    public Control? Build(object? param)
+    {
+        if (param is null) return null;
+        var name = param.GetType().Name!.Replace("ViewModel", "");
+        var type = Type.GetType("Ursa.Demo.Pages."+name);
+        if (type != null)
+        {
+            return (Control)Activator.CreateInstance(type)!;
+        }
+        else
+        {
+            return new TextBlock { Text = "Not Found: " + name };
+        }
+    }
+
+    public bool Match(object? data)
+    {
+        return true;
+    }
+}