HG-122: bunyan logger

Replaced the dummy logger with [bunyan](https://github.com/trentm/node-bunyan).

Currently supported streams are:

* `syslog` - streams the logs to the local `syslog` instance;
* `console` - streams the log to `stdout`, "pretty printed" :tm:; 
* `default` - streams the log to `stdout`, in JSON format;

Streams are controlled by the `loggers` object in `localSettings`. Multiple loggers can be listed: where the key is the stream type and the value is the minimal logging level for the stream. Generally combining `console` and `default` does not make much sense as they both log to `stdout`.