Use of Ferveo for Threshold Signatures and Light Clients

[clvv]

I'm not sure if the following has been discussed or proposed, but I'm putting this into an issue here so we can have a place to discuss things related to this topic.

Once Ferveo is implemented and integrated into the consensus system. It should not be hard to also implement the following:

(1) Threshold (BLS?) signatures
(2) Compact certificates of finalized states using threshold signatures.
(3) Light clients that rely on verification of public key updates and state certificates.

[clvv]

To sum up briefly how Ferveo threshold signature can simplify light clients (as per Tendermint Light Client specification): instead of collecting and recording >2/3 of individual signatures from validators in block headers, a single threshold signature (against validator set of current epoch) can be recorded instead.

This likely amounts to some space savings (for blocks) and efficiency improvements (for light clients), using existing infrastructure (once Ferveo is integrated), at the expense of deviating from Tendermint Core. Since Tendermint already utilizes signatures for light clients, using threshold signature is unlikely to be a significant improvement.

[ValarDragon]

Making Tendermint support aggregated signatures at the consensus level & default light client proof generation is also an option, that Tendermint team would probably be incredibly supportive of