Turret upgrade

It turns out that typical defense turrets were using a SMG ...made from
a pipe and a piece of wood.  No wonder they weren't much of a threat to
endgame armor.

So this upguns the typical lab turret to use an MP5 instead, and creates
the new military-grade M4 turret.  With its upgraded actuators, doubled
ammo capacity, increased HP, deadly-looking green paint job, and ability
to reach out with its 5.56 and touch you 36 tiles away*, these ought to
make miloutposts a little more respectable.

*High-powered lights force night raiders out to range 7.  Helps against
rock-throwing terrorists!
Shortens fluff in description

Ought to help it fit in smaller boxes.
Fixes drops, adds spawn

Almost forgot.
Merge pull request #7804 from KA101/turretupgrade

Turret upgrade