RostockMAX belt tensioner with nut captures

I added M3 hex nut captures to the pieces in order to make installation and adjustment possible with only a single tool.

Instead of a single, universal, tensioner design, there are now four. I also added an extruded pad to the top tensioner pieces that help keep them positioned in the hole on the top of the tower.

The source files and STLs are not as nice as they could be, but I continue to be pleased with FreeCAD's ability to import STLs and convert them to usable solids.