Modular Ender 3 Electronics Enclosure v4.2.7

Took the excellent work by KC3D-LLC and modified it:
- Improved screw domes to circular shape (faster to print)
- Improved rear openings to be more accessible (chamfered)
- Repositioned screw domes and rear opening to fit official v4.2.7 silent stepper motherboard by Creality
- Duplicated, repositioned and improved tolerances for ventilator housing
- Improved venting openings in housing
- Added additional rear opening to fit three stage switch (off, 1, 2) for control of ventilators
- Implemented support structures to V-slot elements to prevent inefficient supports created by slicer software starting at the build plate