Compress tx proofs into batch proof

[leonardoalt]

A few potential ideas:

1- Verify tx in a STARK and make a SNARK aggregator (it is used in practice, but I personally don't know how to do this)

2- Verify tx in a SNARK and make a SNARK aggregator (see https://github.com/nalinbhardwaj/ethdosnumber)

3- Verify sequence of txs in a Nova proof and verify the Nova proof in a SNARK. ZoKrates has experimental Nova proofs, but verifying a Nova proof in a SNARK is still ongoing research.

A general challenge in all these approaches is going to be doing it end-to-end, that is, from a Baby Jubjub wallet all the way to verifying the final SNARK in an Ethereum smart contract.