ui: Showing indexing progress in windows task bar

* implemented showing indexing progress in windows taskbar button
* renamed TaskShowStatusDialog
* added "Qt5WinExtras.dll" for windows builds

src/lib_gui/qt/utility/QtWindowsTaskbarButton.h

@@ -0,0 +1,23 @@
+#ifndef QT_WINDOWS_TASKBAR_BUTTON_H
+#define QT_WINDOWS_TASKBAR_BUTTON_H
+
+class QWinTaskbarProgress;
+class QtMainWindow;
+
+class QtWindowsTaskbarButton
+{
+public:
+	QtWindowsTaskbarButton();
+	void setWindow(QtMainWindow* mainWindow);
+
+	void setProgress(float progress);
+	void hideProgress();
+
+private:
+
+#ifdef _WIN32
+	QWinTaskbarProgress* m_taskbarProgress;
+#endif
+};
+
+#endif // QT_WINDOWS_TASKBAR_BUTTON_H