Make three (hopefully simple) changes to non-native fee processing:

1. Add a "foreign reserve" account (owned by the protocol) which can hold non-native tokens.
2. Send non-native token base fees to that account.
3. Burn native token base fees.

For now, the foreign reserve account does not need any ability to spend the funds -- that can be added later.

Note that the foreign reserve account should also be able to receive ICS20 transfers over IBC. This will be necessary for receiving USDN interest for USDN held on Namada (sent from Noble).

Reference discussion on the forums