Openbuilds V-rail solid and STL aluminum extrusion models for DSM, 2020 2040

These are slightly tweaked versions of the Openbuilds models that I changed slightly for easier DSM (direct solid modeling) use (solid *.sat file format). STL mesh models are included as well. To make prototyping easier, I got rid of the notch running down the middle so that you could snap to center more easily, as well as moving the center channel wall out by 0.1mm so that you can just snap and move 7mm to sit flush on the surface. (Be aware of those changes from the actual extrusions if yo