VirtualNotesFolder's config cannot change

We haven't exposed any way to change it.

lib/core/virtual_notes_folder.dart

@@ -40,6 +40,7 @@ class VirtualNotesFolder with NotesFolderNotifier implements NotesFolder {
 
   @override
   set config(NotesFolderConfig conf) {
+    assert(false, "A Virtual Notes Folder Config cannot change");
     conf.save();
   }
 }

lib/features.dart

@@ -0,0 +1,3 @@
+class Features {
+  static bool perFolderConfig = true;
+}