Turret SFX and spawning changes

* Turrets now use the SFX associated with the weapon installed in them
* Turrets now have a default installed gun for when they are spawned
* fire_sound is now a property of all ammunition, not just energy ammo,
which should make future additions a lot simpler.
* Added some energy gun SFX handling to the giant switch statement at
the top of portable_turret.dm, because 'emagged' and 'lethal' are the
same thing and have to be handled weirdly.
* The upshot of all these changes is that every turret, constructed or
default, should make exactly the right noise, even if guns are added in
the future!