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

…go prices. (shiptest-ss13#2795)

<!-- Write **BELOW** The Headers and **ABOVE** The comments else it may
not be viewable. -->
<!-- You can view Contributing.MD for a detailed description of the pull
request process. -->

As the name says.

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.

: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:

<!-- Both :cl:'s are required for the changelog to work! You can put
your name to the right of the first :cl: if you want to overwrite your
GitHub username as author ingame. -->
<!-- You can use multiple of the same prefix (they're only used for the
icon ingame) and delete the unneeded ones. Despite some of the tags,
changelogs should generally represent how a player might be affected by
the changes rather than a summary of the PR's contents. -->