Jo Presser alternate parts (M8 idler and feet)

The design by Vector3D is very good, but I needed to make some minor tweaks to fit the spare parts I had on hand from a broken Ender 3. The feet attach to the sides of the extrusion and can be printed on most printers, even teeny tiny ones. The idler attaches the same as the original, but is fit for the hardware that an Ender 3's idlers use.