BlockId removal: tx-pool refactor

It changes following APIs:
- trait ChainApi
-- `validate_transaction`

- trait `TransactionPool`
--`submit_at`
--`submit_one`
--`submit_and_watch`

and some implementation details, in particular:
- impl `Pool`
--`submit_at`
--`resubmit_at`
--`submit_one`
--`submit_and_watch`
--`prune_known`
--`prune`
--`prune_tags`
--`resolve_block_number`
--`verify`
--`verify_one`A

- revalidation queue

All tests are also adjusted.