Adds Underbarrel shotguns as attachment to some vanilla guns.

Current Underbarrel shotguns:
-Spas 12
-SIX 12

Currently supported vanilla weapons:

-M14

-M4A1

-M16

-K23B

-AKSMU

-MP7

-CR805

-UMP

-G36

-AK5

-AUG

-SCAR

-FAL

-G3

-Colt 733

-Galil

-L85A2 (only with EAC or the L86 LMG conversion mods)

-VHS-D2

-ASVAL

-HK416C

-RPK

-AKM

-AKM Gold

-AK74

-Saiga

-Six12

-Sg552

-AK12

-F2000

-TR-1

-DTA Stealth Reacon Scout

-UZI

We currently can't have better animations for this, so we have to use what we have.
Some akimbo weapons can equip this, but on switching to the underbarrel you'll only get a single gun with said underbarrel switching back reactivates both akimbo guns. This isn't intentionally, currently there is no way around this.

The Iron sights are intentionally off when you equip the underbarrel shotgun, I could change that if enough ppl complain about the current method.