Showing message in main window's status bar.

        This also changes mouse cursor to Qt.WaitCursor

def starting_long_process(self, message):
        """
        Showing message in main window's status bar.

        This also changes mouse cursor to Qt.WaitCursor
        """
        self.show_message(message)
        QApplication.setOverrideCursor(QCursor(Qt.WaitCursor))
        QApplication.processEvents()