Feature: remove signers or refresh shares with trusted dealer

[natalieesk]

Motivation

There may be situations where you may want to remove signers.

Design

To do this you would need to perform a resharing protocol and leave out the relevant participant.

This is done by basically redoing the trusted dealer generation with a "zero" secret, and adding the new shares to the old ones, while keeping only the participants that are wanted

References

[chelseakomlo]

I changed this issue to "remove signers or refresh shares" since the technique is the same.

[chelseakomlo]

Completed

[conradoplg]

Reopening, we just implemented repair share, refresh/remove is still missing

[mpguerra]

@natalieesk can you please split this one up and we turn it into a tracking issue instead