Optimise light client signature verification

[adrianbrink]

Full nodes when responding to light-clients should send signatures in descending order by voting power. In most instances it is enough to validate <1/2 of the signatures given that there is some concentration of voting power at the top. This will make light-clients much more bandwidth and energy efficient.

[jackzampolin]

Light client signature verification is currently only used for accounts. There is much more work to make this feature general. I'm going to go ahead and close this issue as we still need to go through the spec/impl process for this feature.

[ValarDragon]

No, this is different from lite client state queries. Lite client verification is needed for block headers as well. This is something we should absolutely do. tendermint/tendermint#2478 is all about optimizing this exact thing.

This is not for state queries, this is for getting the most recent state hash.

[jackzampolin]

Going to close this issue as there is fundamental work to be done on the lite client before we optimize.

[ValarDragon]

Lets write this down somewhere as an explicit goal in the lite client verification?