GAE Module support for Furious

Given the way that [GAE Modules](https://developers.google.com/appengine/docs/python/modules/) directs traffic to the main application or sub-modules, if furious exists in both places, a prefix needs to be added to the furious endpoint to make sure it executes the correct code.

To make this easier, adding a FURIOUS_URL constant to settings.py will allow users to direct the appropriate furious traffic to the correct, related endpoint.