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.
Parameter expansion is still performed even with `=~`.  It doesn't make sense to have an identifier after `$` if you mean `$` in the regex sense, and shell leaves `$` as literally is if it is not followed by an identifier, so I guess we just luck out here that regex syntax picks up exactly where shell drops off.