[WIP] Classic zombie pack

Adds mundane "variations" of regular regular zombies. Classic mode friendly.

*Fat zombie: Stumbling as it moves, this corpse of an overweight human regards it's surroundings with an empty black gaze.*

Takes up about 26% of regular zombie spawns.While tougher then regular zombie, its slow speed makes it a lot less dangerous.

*Strong zombie: Once an able-bodied human, now a monster, whose facial expression is twisted into one of rage.*

Takes up about 10% of regular zombie spawns. Faster, tougher and stronger, but not by much.

(Additional note: child zombies were set to take about 10% of regular zombie spawns)

*Decayed zombie: An once-dead body of human. Its discolored swollen flesh is riddled with festering wounds and open sores.*

Takes up about 6% of regular zombie spawns. Same problem as with Rot-weiler, so I gave it "VENOM" flag too.

*Crawling zombie: Having lost control of lower part of body, this zombie slowly drags itself by its arms.*

Takes up about 3% of regular zombie spawns. Has an abysmal movement speed and can grab if able to reach you. 

*Hazmat zombie: This human is completely cowered in a torn protective suit. Only the unsteady gait betrays it's true nature.*

Drops various environmental protection gear and is immune to acid by itself.

Feel free to suggest improvements and more classic zombies.