Implement a column sort.

def sortByColumn(self, index):
        """Implement a column sort."""
        if self.sort_old == [None]:
            self.header_class.setSortIndicatorShown(True)
        sort_order = self.header_class.sortIndicatorOrder()
        self.sig_sort_by_column.emit()
        if not self.model().sort(index, sort_order):
            if len(self.sort_old) != 2:
                self.header_class.setSortIndicatorShown(False)
            else:
                self.header_class.setSortIndicator(self.sort_old[0],
                                                   self.sort_old[1])
            return
        self.sort_old = [index, self.header_class.sortIndicatorOrder()]