Support configuring loggers as described in issue #413

[pierredelisle]

(https://github.com/actions-on-google/actions-on-google-nodejs/issues/413).

With that change, a client application that uses Firebase cloud functions would simply need to do the following to improve substantially the readability of log entries in the cloud functions logs console:

const app = smarthome({   debug: true,   logs: {     debug: functions.logger.debug,     info: functions.logger.info,     // 'warn' maps to 'error' in firebase logs.     // If set to functions.logger.warn, there is no level associated with the log entry.     warn: functions.logger.error,     error: functions.logger.error   } });

[Fleker]

You may be interested in looking at a similar commit done to the assistant/conversation lib