Sort songs in collection by song title instead of track if previous

grouping is not the album.

Fixes #295

src/collection/collectionmodel.h

@@ -251,6 +251,7 @@ class CollectionModel : public SimpleTreeModel<CollectionItem> {
   QVariant data(const CollectionItem *item, int role) const;
   bool CompareItems(const CollectionItem *a, const CollectionItem *b) const;
   int MaximumCacheSize(QSettings *s, const char *size_id, const char *size_unit_id, const int cache_size_default) const;
+  bool IsAlbumGrouping(const GroupBy group_by) const { return group_by == GroupBy_Album || group_by == GroupBy_YearAlbum || group_by == GroupBy_OriginalYearAlbum || group_by == GroupBy_AlbumDisc || group_by == GroupBy_YearAlbumDisc; }
 
  private:
   CollectionBackend *backend_;