Complete Rework of Gun code + Flare guns

- Added the flare gun, which fires flare shells (also shotgun compatible) and a syndicate version (for atmos techs) capable of firing both flares and shotgun shells
- Reworked the way guns work, splitting ammo_storage into 3 types with their own details. Empty_magazine is gone, and automatics now properly accept and remove magazines
- Automatics have a new verb : toggle burstfire. Burst fire makes you fire a lot of bullets at once, but with a long cool-down
- Added a box of flares to let you carry a few around
- Made shotguns now eject empty shells, which can be used to make new shells
- Attempting to load a gun from an ammo box now requires you to stand still or you don't load then and drop some bullets