Returns the index of the inputed action.
        
        :param      action | <QAction> || None
        
        :return     <int>

def indexOf(self, action):
        """
        Returns the index of the inputed action.
        
        :param      action | <QAction> || None
        
        :return     <int>
        """
        for i, act in enumerate(self.actionGroup().actions()):
            if action in (act, act.objectName(), act.text()):
                return i
        return -1