Sets the columns for this gantt widget's tree to the inputed list of
        columns.
        
        :param      columns | {<str>, ..]

def setColumns( self, columns ):
        """
        Sets the columns for this gantt widget's tree to the inputed list of
        columns.
        
        :param      columns | {<str>, ..]
        """
        self.treeWidget().setColumns(columns)
        item = self.treeWidget().headerItem()
        for i in range(item.columnCount()):
            item.setTextAlignment(i, Qt.AlignBottom | Qt.AlignHCenter)