Run folder search filtering in the background

It uses the same approach used by the comics search filter

YACReaderLibrary/db/folder_query_result_processor.h

@@ -0,0 +1,36 @@
+#ifndef FOLDER_QUERY_RESULT_PROCESSOR_H
+#define FOLDER_QUERY_RESULT_PROCESSOR_H
+
+#include <QObject>
+
+#include "yacreader_global_gui.h"
+#include "concurrent_queue.h"
+
+class FolderItem;
+class FolderModel;
+class QSqlQuery;
+
+namespace YACReader {
+
+class FolderQueryResultProcessor : public QObject
+{
+    Q_OBJECT
+public:
+    FolderQueryResultProcessor(FolderModel *model);
+
+public slots:
+    void createModelData(const SearchModifiers modifier, const QString &filter, bool includeComics);
+
+signals:
+    void newData(QMap<unsigned long long int, FolderItem *> *filteredItems, FolderItem *root);
+
+private:
+    ConcurrentQueue querySearchQueue;
+
+    FolderModel *model;
+
+    void setupFilteredModelData(QSqlQuery &sqlquery);
+};
+};
+
+#endif // FOLDER_QUERY_RESULT_PROCESSOR_H