{Reviewer: Matt} NOT TO BE MERGED - Update Sprout to match new Homestead APIs

Matt,

This covers the Sprout updates to match the new Homestead API. It passes "make test" and I've also run stress against it which seems to work effectively. I can't run the live tests, as a deployment with these changes is currently incompatible with Ellis.

As discussed, the main principle is changing get_associated_uris and get_user_ifc into one get_subscription_data method, and caching the result of that in the UASTransaction object.