Spreading Stun Shells and Riot Shotguns

-Adds a new shotgun shell that fires stunning pellets.  (Read:  The horrific offspring of a Buckshot shell and a taser)
-Adds a riot shotgun that starts with the new shells and replaces the current riot shotguns in the armory.
-The new shell type can be made in the protolathe.
-Riot shotguns can be ordered from cargo.