Override Qt method

        Add/remove breakpoints by single click.

def mousePressEvent(self, event):
        """Override Qt method

        Add/remove breakpoints by single click.
        """
        line_number = self.editor.get_linenumber_from_mouse_event(event)
        shift = event.modifiers() & Qt.ShiftModifier
        self.editor.debugger.toogle_breakpoint(line_number,
                                               edit_condition=shift)