NotesFolder: sort the sub-folders

This really isn't a good way of doing this as now the folder
inserted/removed notifications will not be correct. But at least the
folders will be sorted.

lib/core/notes_folder.dart

@@ -106,6 +106,8 @@ class NotesFolder
   }
 
   List<NotesFolder> getFolders() {
+    // FIXME: This is really not ideal
+    _folders.sort();
     return _folders;
   }