Isolate/namespace command computer IDs

[SoniEx2]

Command computers should have their own ID namespace, separate from normal computers. This would allow them to be a little more trusted with secrets than a normal computer. In particular, this would make it effectively impossible to exfiltrate secrets without op, even if the player had access to creative, /data, /give, and /setblock.

[tonitch]

Could the command computer's ID be negative? I believe this is an elegant solution.