Security issues about nanofusion

[unyieldinggrace]

@PlasmaPower thanks for the code-review and feedback points. I'm taking a couple of days off from coding to give myself rest, but will certainly get on them. There are some bits that I consider as belonging in the "won't fix" pile (or at least "not my problem" pile). Masking IP addresses is a great idea, but I think it's something that realistically needs to be left to the end user, not baked into NanoFusion. I'm prepared to be persuaded otherwise, but that's my thinking for now.

I hadn't quite worked out the point of the zValue. The scheme "works" if zValues are all empty, which is why I thought it was fine to calculate deterministically (also helped me with debugging, because output was consistent each time I ran it). I see now that it's meant to be a random variable to prevent key re-use attacks. Thanks for pointing that out.

[unyieldinggrace]

The issues with R commitments not being validated should now be fixed in the mixing context. The PhaseTracker should prevent moving on to signing until all commitments are checked.

[PlasmaPower]

Thanks, I'm liking the new phase architecture a lot better :)