Reduce includes

src/core/application.h

@@ -28,7 +28,6 @@
 #include <memory>
 
 #include <QObject>
-#include <QThread>
 #include <QList>
 #include <QString>
 
@@ -36,6 +35,8 @@
 
 using std::unique_ptr;
 
+class QThread;
+
 class TaskManager;
 class ApplicationImpl;
 class TagReaderClient;