We need to have BLS signed Pool State

Currently we have BLS signature over Domain State (domain ledger transactions) only, that is over NYM, CLAIM_DEF, SCHEMA, etc.
We need to have BLS muli-signature support over Pool State (pool ledger transactions such as NODE) as well to be able to perform catch-up more efficiently. With BLS multi-signature for Pool state, we could catch-up from on node and make sure that this is a valid state.
Find more details in Observer Architecture.