Esper foregrip remix

This is a replacement Foregrip for the Esper. It allows for 3 metal support rods to be used vs the standard Esper set-up.

It also allows for a Worker Power barrel to be installed with the standard Caliburn Muzzle and Trench. The Foregrip has been shortened to accommodate barrel and draw.

version I - Priming rod slots too small. Update pending.

version II - Slots corrected. Added texture to sides.

version III - nut slot created for dropping in 10-32. moved priming bar slots inwards.