Add Limited Ammunition and Ammo Scavenging to Zombies

Zombies currently has a difficulty problem: once players find a safe camping position, such as the Asylum elevator, they can survive with very little risk. Since zombies do not become significantly stronger with each round and weapons cannot be repurchased, infinite ammunition removes much of the pressure from reaching higher rounds. Limit ammunition so players eventually need to leave their defensive positions and search the map for supplies. Ammunition could be obtained from scattered crates or mystery-box-style sources, keeping players moving and creating more meaningful decisions. This could also reduce the need to constantly increase the number of zombies or place additional spawn points throughout every map. If implemented, the starting pistol should provide a generous amount of ammunition so new players have enough time to explore and acquire better weapons.