Warn before software closed; fix bug on first run

Also put settings into proper dir

src/ViewModels/ShutdownCheckViewModel.cs

@@ -0,0 +1,29 @@
+#nullable enable
+
+using DialogHostAvalonia;
+using MayShow.Models;
+
+namespace MayShow.ViewModels;
+
+class ShutdownCheckViewModel
+{
+
+    public ShutdownCheckViewModel()
+    {
+    }
+
+    public void SaveAndShutdown()
+    {
+        DialogHost.Close("DialogHost", ShutdownCheckOptions.SaveAndShutdown);
+    }
+
+    public void DoNotSaveAndShutdown()
+    {
+        DialogHost.Close("DialogHost", ShutdownCheckOptions.NoSaveShutdown);
+    }
+
+    public void CancelShutdown()
+    {
+        DialogHost.Close("DialogHost", ShutdownCheckOptions.CancelShutdown);
+    }
+}