Create a message box, that asks the user to continue although files have been modified

        :returns: value of the standard button of qmessagebox that has been pressed. Either Yes or Cancel.
        :rtype: QtGui.QMessageBox.StandardButton
        :raises: None

def doc_modified_prompt(self, ):
        """Create a message box, that asks the user to continue although files have been modified

        :returns: value of the standard button of qmessagebox that has been pressed. Either Yes or Cancel.
        :rtype: QtGui.QMessageBox.StandardButton
        :raises: None
        """
        msgbox = QtGui.QMessageBox()
        msgbox.setWindowTitle("Discard changes?")
        msgbox.setText("Documents have been modified.")
        msgbox.setInformativeText("Do you really want to exit? Changes will be lost!")
        msgbox.setStandardButtons(msgbox.Yes | msgbox.Cancel)
        msgbox.setDefaultButton(msgbox.Cancel)
        msgbox.exec_()
        return msgbox.result()