Bracket for MRServo model railroad switch machine

A convenient mounting bracket for [Iowa Scaled Engineering MRServo](http://www.iascaled.com/MRServo) servo-based model railroad switch machines (all variants after Dec 2017, and -2/-3 units before that). Holds both the control board and 9g servo in one convenient mount, with slotted screw holes for easy adjustment. Look at our other things for a MRServo-1 bracket for MRServo units before Dec 2017 and a "just a 9g servo" bracket.

The part was designed in Fusion 360, but I've included the ori