Create Aggregated Feed #63
Description
A feed which is the automatic aggregate of all of a user's feeds should be created.
This can be modeled as a feed that subscribes to all of a user's other feeds, which would allow us to drop the user_subscription table, and properly track subscription changes across time while avoiding additional complexity due to possible duplicates that would have occurred if a user's subscriptions were tracked in one global table, rather than being aggregated "just in time" from a user's existing feeds.
The aggregate feed should list all of a user's feeds that exist (except itself), and implicitly subscribe to all of them to generate an aggregate feed.