2.2 install premium carts

Enable all the bits that make it possible to enable the premium cartridge channels as needed based on cartridges requested. Some refactoring was needed; also there were some lingering references to 2.1 channels.

Although we can't really use any of this until 2.2 channels are live, I'd like to be testing with these changes in place ASAP to catch any regressions.
Fair enough :)