Support deterministic builds of whole environment

[patcon]

First off, this is really rad. Just wanted to say that. Thanks Geneva!

I've only looked briefly, so maybe this is already underway.

The idea would be to generate the environments used to carry out all these procedures in a totally deterministic way. So build all the tools used from source, and verify signatures, and provide an environment that citizens can rebuild and check those signatures themselves.

This would be similar to how the Bitcoin build process works, and the tools they've built to support that:
https://github.com/bitcoin/bitcoin/blob/master/doc/gitian-building.md