pycctx: mixed mode

[Alrighttt]

I believe we need CC mixed mode implemented into pycctx for it's spam prevention features.

I have merged mihailo's cc_mixed_dev branch into my pycc branch, and komodod is able to redirect the validation to pycc cc_eval as expected. However, pycctx, as far as I can tell, gives no way to produce/sign CC mixed mode conditions.

I am opening this issue as a place to discuss whether we will implement CC mixed mode. If so, to discuss who can work towards implementing it. If not, to discuss viable alternatives for spam prevention.