Proofs can be submitted off-chain to save more time

[hatark]

As @zkrollupdev suggested, users' proofs can be directly submitted off-chain, then submit an aggregated proof on-chain. I think this is a good suggestion, both at user experience and technical feasibility.

We can remove the submit_proof method. Add more check to submit_batch to ensure that the aggregated proof consists of all the proofs it claims. We alse need a submit proof service API to receive all the submits from users.