[Bug] Toggle Stack Trace

#### Problem

Currently when an error occurs in a **batch request**, the stack trace of the exception is included in the body of the JSON response. 

#### Solution

Toggle this behaviour based on a `debug` value in the config hash handed to the Broker (defaults to **false**).

![image.gif](http://media.giphy.com/media/ePYyTwoGI50aY/giphy.gif)