[PR] Airlock packet protection, take two

[Studenterhue]

Merged just yesterday. Barring a minor rename of a define, it's about same as described in the original post: hacking doors via packets now requires sending an access code. It can change when the AI control wire is pulsed, and for now it's simply a random number between 1 and 32, rather than the math ideas.

Pali has said on the PR discussion that he's willing to make access codes on important airlocks more difficult in some way so please make a thread or direct feedback his way if you desire such.

I think I'm gonna try this version and maybe increase difficulty on important airlocks later based on feedback for this.