ATH-M50(X) Replacement Hinge

The hyperair's version slightly did not match my m50. I changed the model for my headphones.

Changes:

1. Reduce bar size for 5mm (23.87 -> 18.87)
2. Reduce hinge pins diameter
3. Add flat part to hinge pins
4. Fix the list of included files to match the current dev branch of the MCAD library.