Give users a way to prove they aren't cheating

[duxovni]

When another user takes too long to reply or gets disconnected during a time-sensitive stage of the SENPAI protocol, we currently flag them as cheating, but this could just be a problem with the server or with their internet connection. We should give users a "recovery phrase" that they can pass on to their partner if they get disconnected, containing either s or x depending on which role the user is playing in the protocol. The client will allow users to complete the answer-sharing and honesty-proving stages out-of-band if necessary, by exchanging these phrases over any medium they choose.

[cryslith]

I don't think anyone's going to complete anything out-of-band. It would make more sense to add some server-side persistence to allow resuming an incomplete exchange.

[duxovni]

Fair point; this can probably be dealt with as part of fixing #6 , since there'll need to be a lot of state saved on the server in any case.