Iterates over the `watched_configurabes` attribute and starts a
        config file monitor for each.  The resulting observer threads are
        kept in an `observers` list attribute.

def start(self):
        """
        Iterates over the `watched_configurabes` attribute and starts a
        config file monitor for each.  The resulting observer threads are
        kept in an `observers` list attribute.
        """
        for config_class in self.watched_configurables:
            monitor = ConfigFileMonitor(config_class, self.config_dir)
            self.observers.append(
                monitor.start(
                    self.add_configurable,
                    self.update_configurable,
                    self.remove_configurable
                )
            )

        wait_on_event(self.shutdown)