Client id for stat tracking

[aufau]

Provide unique client id to servers for simple tracking systems in serverside mods.

Either port ja_guid from OpenJK that provides rudimentary safety from impersonation attempts, but the id is different on each server (changes with server ip/port). This probably could be ported to a qvm mod so it's a bit superfluous.

Or use a public-key cryptography approach where client has a single public key as its id for all servers and authenticates using matching private key. This is better (single id allows cross-server tracking), safer and can't be ported to mod easily because cryptographic libraries depend on 64bit integer variables.

This requires designing authentication protocol and embedding it into existing connection protocols.

[aufau]

Note: It seems ja_guid OpenJK implementation isn't safe after all. Secret key or equivalent can be probably extracted.