Additional ammo in the extra items store.

[Erick Maksimets]

Add the ability to purchase ammo for standard weapons. 30 bolts for a crossbow, 50 rounds for a shotgun, 300 rounds for everything else. +3 alternative ammo for smg

I think the price of 7 ammo packs will be fair.

[Nicksf13]

https://github.com/Nicholas-Fuchs/zombieplague/tree/ZP-212 - Can you test it?