Randomize amount of ammo in gun spawns and other small fixes for zombie soldiers loot spawn

[Night-Pryanik]

Summary

SUMMARY: Balance "Randomize amount of ammo in gun spawns."

Purpose of change

Made it so guns spawn not only full or empty, but with random number of bullets in them.
Initially I just wanted to randomize only amount of bullets in zombie soldier's guns, but then I noticed other issues like guaranteed spawn of cash cards or fixed amount of charges in matchboxes. So I decided to fix these too while I'm here.

Describe the solution

• Added "charges-min": 0, "charges-max": XX" fields for almost every type of gun in guns.json, where XX is the maximum number of bullets allowed for standard magazine for the gun in question.
• Also made a small balance change: I capped maximum number of bullets allowed for spawn in machine guns to 100 even if they could contain 500.
• Randomized number of matches in matchboxes, charges in gas masks, rolling paper and rolling tobacco.
• Decreased chance to spawn cash cards on zombie soldiers and zombie pilots loot from guaranteed to 10%.