BfB3000 Vertical spool holder

This thing is a 50mm diameter spool holder for vertical mount on a BfB3000 (or BfB Touch hopefully).
Inspiration comes from Gael Langevin so I want to thank him for that.

Under the exact same slicing conditions, this derivative uses :
- much less plastic (28.58 cm3 instead of 49 cm3)
- and much less time to print (2h48mn instead of 5h18mn)

And I believe it should be pretty much as strong (but I haven't tried Gael's design).

The 2 parts will fit together using 2 screws (5mm in diamete