Bitcoin two face

This has been fully remodeled inspired by karilawler version.

The changes include:
- Simpler polygons geometry in termos of the 'B' and groves around it resulting on faster prints.
- 3.5mm thickness with 0.8mm groves
- 40mm diameter
- 2 sided

The result shown in the pictures are using the following settings in Cura 4.4:

- Layer Height: 0.2mm
- Line Width: 0.4mm
- Wall Thickness: 1.2mm
- Wall Line Count: 3
- Bottom Layers: 9999
- Infill 100%

- Print Speed: 60 mm/s