[fork2022] types: introduce unburn and ungift addresses

(To activate this change, set types.Fork2022 = true.)

This address is replaced with burn address in UnlockConditions.UnlockHash() method, so all other code treats this address as if it was burn address. The wallet owning unburn address sees coins sent to burn address and can sign transactions spending burnt coins. Consensus code accepts signatures made by unburn address af if they were made by burn address.

Ungift address is similar to unburn address, but for AirdropNebulousLabsUnlockHash.