avalonia: Added progress indicator

InABox.Avalonia/Navigation/Navigation.cs

@@ -12,6 +12,8 @@ public interface IViewModelBase
     Task Activate();
     Task Deactivate();
     bool BackButtonVisible { get; set; }
+    
+    bool ProgressVisible { get; set; }
     AvaloniaMenuItemCollection PrimaryMenu { get; set; }
     AvaloniaMenuItemCollection SecondaryMenu { get; set; }
 }