Simplified GT2560 case

I loved lukie80's case design, but I had a few issues with it. I prefer to print smooth holes and tap them using a hand tap. This gives me great threads without the hassle of a complex model (original stl had ~ 211,000 entities, this version has 43,000)

I also eliminated to 90 degree angles on layer 1, I was having a lot of trouble getting it to stick for some reason. Maybe time to look at my acceleration settings.

Prints in 4 hours with a 0.6 nozzle and 0.4 layers

This is based on the 81mm version.