Add Blaze's Turret mod

per http://smf.cataclysmdda.com/index.php?topic=8060.msg190017#msg190017

This is the Vehicle Turret Mod, by Blaze. I have not done any work on this other than submitting it here, so all credit goes to Blaze.
Artificial, and $20K ($20,000.00, as specified) is pretty expensive post-Cataclysm.  May well be worth it--haven 't tried the unit--but wanted to point that out.