Clean the logs list by deleting finished items.

        By default, only delete WARNING message.
        If critical = True, also delete CRITICAL message.

def clean(self, critical=False):
        """Clean the logs list by deleting finished items.

        By default, only delete WARNING message.
        If critical = True, also delete CRITICAL message.
        """
        # Create a new clean list
        clean_events_list = []
        while self.len() > 0:
            item = self.events_list.pop()
            if item[1] < 0 or (not critical and item[2].startswith("CRITICAL")):
                clean_events_list.insert(0, item)
        # The list is now the clean one
        self.events_list = clean_events_list
        return self.len()