added new view for empty folders in YACReaderLibrary that shows a list with all the subfolders

TODO ?use a special case for the root folder?

YACReaderLibrary/db_helper.h

@@ -51,6 +51,7 @@ public:
 	static ComicDB loadComic(qulonglong id, QSqlDatabase & db);
     static ComicDB loadComic(QString cname, QString cpath, QString chash, QSqlDatabase & database);
 	static ComicInfo loadComicInfo(QString hash, QSqlDatabase & db);
+    static QList<QString> loadSubfoldersNames(qulonglong folderId, QSqlDatabase & db);
 };
 
 #endif