Do not write the title as h1 if it is in the yaml header

In general, we try to follow the conventions in the note parsed over
whatever the default config.

Related to #214

lib/core/note_serializer.dart

@@ -148,6 +148,7 @@ class NoteSerializer implements NoteSerializerInterface {
       note.title = emojiParser.emojify(title);
 
       propsUsed.add(settings.titleKey);
+      settings.saveTitleAsH1 = false;
     } else {
       var startsWithH1 = false;
       for (var line in LineSplitter.split(note.body)) {