Warn before software closed; fix bug on first run

Also put settings into proper dir

src/Views/ShutdownCheckView.axaml.cs

@@ -0,0 +1,14 @@
+using System;
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Markup.Xaml;
+
+namespace MayShow.Views;
+
+public partial class ShutdownCheckView : UserControl
+{
+    public ShutdownCheckView()
+    {
+        this.InitializeComponent();
+    }
+}