Warn before software closed; fix bug on first run

Also put settings into proper dir

src/Interfaces/ICanCheckShutdown.cs

@@ -0,0 +1,8 @@
+using System.Threading.Tasks;
+
+namespace MayShow.Interfaces;
+
+interface ICanCheckShutdown
+{
+    Task<bool> CheckIsSafeToShutdown();
+}