Adds the inputed logger to the list of loggers that are being tracked
        with this widget.
        
        :param      logger | <logging.Logger> || <str>
                    level  | <logging.LEVEL>

def addLogger(self, logger, level=logging.INFO):
        """
        Adds the inputed logger to the list of loggers that are being tracked
        with this widget.
        
        :param      logger | <logging.Logger> || <str>
                    level  | <logging.LEVEL>
        """
        if isinstance(logger, logging.Logger):
            logger = logger.name
        
        if logger in self._loggers:
            return
        
        # allow the handler to determine the level for this logger
        if logger == 'root':
            _log = logging.getLogger()
        else:
            _log = logging.getLogger(logger)
        
        _log.addHandler(self.handler())
        
        self._loggers.add(logger)
        self.handler().setLoggerLevel(logger, level)