Direct Drive Extruder Servo Mount Improved

This is a slightly improved version of Gumpwa Luong's Servo Mount (thing # 559745) for Marty Rice's awesome Direct Drive Extruder (thing # 501755). The servo is used to implement Auto Bed Leveling.

All dimensions are the same as Gumpwa's original part. I added guide holes for the servo's small self-threading screws (usually included with the servo itself), nut traps for the two M3 nuts that hold the mount to the extruder body, and a couple of reinforcements. I also fixed a possible printing