Adds new ammo boxes, adds them to cargo and granularizes ammo box car…

…go prices. (#2795)

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## About The Pull Request

As the name says.
## Why It's Good For The Game

More ammo boxes are good i think. Makes more types of ammo less
incredibly expensive to use. Guns have already been granularized and as
such i think doing the same for ammo boxes is appropriate.

## Changelog

:cl:
add: Ammo boxes for 4.6, 8x50, Ferromagnetic slugs, pellets, lances and
8x50 Hollow Points!
balance: Granularized ammo boxes in cargo in a similar way to guns.
/:cl:

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