Dismemberment Update, Fireaxe Fixes, Gunshot Sound Changes

- Dismemberment update, phase one:
Only melee weapons currently cause dismemberment, because projectile-based weapons causing dismemberment has been a major balance issue -- especially with Nuclear Operatives.
Once I've got more time to properly look at it, I plan to add dismemberment to a human's ex_act() as well, so explosions dismember humans. Expect updates on that tomorrow.

- Fire axe icon fix, it should no longer be invisible.

- Several guns now use a different sound effect.