Shaiss Back Plate for 80mm fan with fixed Screw Wall thickness for better slicing

I added about 0.3 to .5 thickness to Screw walls to fix the slicing issue.

This design was added to the original thing files: http://www.thingiverse.com/thing:1557245 since it was just a minor tweak of Shaiss' work and it keeps the files in one spot making it easier for you guys to find the right file.

It came out nicely.

Thanks for this design!