Various gun stuff

Adds chamber to mag-type guns.
Ammo now loading into the chamber.
Adds some new sprites for ammo mags.
Renamed load_into_chamber() to process_chambered()
UZI, Saber and Stechkin now have states without magazine and without bullet in chamber.
Added sprite of live ammo casing.
Shotguns now spents shells instead of replacing them with empty shell
Fixes magazine's loading. Now you can't load stechkin with SMG mag
Now you can load bullet in chamber and unload it

This is my first (actually second) pull request , so please, don't throw shit on me
Yep, now it adds special overlay and removes BB from casing