E3D, stock and dual XYZ Da Vinci Jr Mounting Brackets

This is a Remix of kr15_uk's E3D bracket for the Da Vinci Jr that ports it to OpenSCAD, and adds several variations of mounting bracket for:

- Stock Da Vinci Jr hotend
- E3D Lite6 (should also work with all-metal E3Dv6)
- Dual: E3D Lite6 + Stock Da Vinci Jr (with adjustable stock hotend height)
- Dual: 2x E3D Lite6
- Dual: 2x E3D Lite6 back-to-back (compact)

Also included is a blank Da Vinci Jr mounting bracket model that can be used to create additional Da Vinci Jr quick-release mount