updates spawners + reach and centcomm (#4)

## About the PR
Further refines the item spawners. There is now a separate group for
utility items & ammo, and significantly more weapons available.
Effectively, almost every viable weapon that isn't total dogwater or
completely unfun to fight has been added to the pool.
Ammo rarity being weird has been fixed (no more random caseless mags and
antimateriel spam.)
The Nuclear Option has been re-introduced, but is now much rarer.

Updates reach & centcomm to add the new spawners. I don't feel like
doing train right now.

## Why / Balance
more weapons = more variety
more granularity with spawners = more balanced ammo & utility spawns

## Technical details
N/A

## Media
N/A

## Requirements
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- [X] I have added media to this PR or it does not require an ingame
showcase.
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## Breaking changes
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class/method/field changes, prototype renames; and provide instructions
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**Changelog**
:cl:
- add: Further enhanced item spawners. Utility items & ammo should now
spawn in a more balanced manner, and almost every reasonable-to-add
weapon in the game is now available.
- fix: Caseless mags will no longer spawn in the ammunition pool.