return error on verification functions

[fedekunze]

On the SDK implementation, we updated ICS23 to return an error when the verification failed. Would it be possible to do the same here now that we doing the migration?

cc: @cwgoes @AdityaSripal

https://github.com/confio/ics23/blob/9f53dd0c42123f18211f8671500d257696fd32e0/go/ics23.go#L36

https://github.com/confio/ics23/blob/9f53dd0c42123f18211f8671500d257696fd32e0/go/ics23.go#L52

[colin-axner]

It turns out, without needing to support compressed or batch proofs, we can use the proof.Verify(...) function directly. I've updated that in ibc-go here. We are choosing not to change the VerifyMembership and VerifyNonMembership functions to avoid unnecessary disruption (as it is a breaking change)