put enemy and player bullets on different layers

bullets don't collide with each other anymore (was preventing scattershot form working properly because they would kill each other when clumped  together)
changed scattershot's spread from 60 to 45 degrees
fixed two issues with scattershot and ammo

player now auto-reloads if shooting with 0 ammo
player no longer shoots lopsided scattershots if the amount of ammo we have is less than what scatter can shoot