How to collect honest participants with signers including malicious signer

[Yamaguchi]

Reported in #29

If a malicious signer participates sharing VSS process and they does not participate sharing local signature process, then no one can submit blocks.
It is better that we have some scheduled sub-round to wait enough (over threshold) participants in one round.

[Yamaguchi]

This problem is caused by not only malicious signers. Honest signers can make the same situation if their signer process accidentally stops