Bicycle wheel truing stand remix for fatbike rim

This is a remix of the great thing from @Hardy, thanks for the design. I needed to modify the original thing so that it could fit my 80mm fatbike rim.

Changes:

• enlarged the gears to 52.5mm and created rimgrabber_gear_d variable
• longer grabber arms
• M8 nut diameter to 12mm, the M8 nuts here in Finland are smaller than the original 13mm
• some assorted mods to the OpenSCAD source, like code stylizing for me to read better

Everything works as in the original thing so please follow the instructions there.