Allow use of Django debug toolbar with JSON views

Usage example: http://localhost:8000/json/Spark/2014/stats?json_debug

@benjaminjkraft, have fun with the query optimization.
This now means that ``@json_response`` can only be used with the json data module. However, this decorator is being used in other modules.

Can you put the template file in a non-program module-specific location? Or else restrict this feature to use in the JSONDataModule?