Add Survival, a gamemode where randomly selected hunters must frag all the survivors without being caught

Implements the Survival gamemode where every player appears the same colour but some are imposters, ala TTT/Among Us. Hunters must hunt down all the survivors without outing themselves as a hunter.
Survivors who incorrectly guess the hunter by killing a fellow survivor will also be killed (this feature can be turned off).

Scoring (default):
1 point is awarded for surviving until the hunters are eliminated or the round time limit is reached.
1 point is awarded for each survivor killed while playing as a hunter.
First player to reach the point limit wins.


Things that need addressing:
Survival status is sent to clients, this could potentially allow cheating. May be easy to resolve by checking if the player is a survivor and marking status as private to fellow survivors.
Teamkill scoring is poorly handled; scores are given to counter the score taken for teamkills. This could be solved by extending the teamkill code to allow disabling the score reduction, potentially useful regardless.