Customizable spider core (1-30 arms)

n-arm spider arm core, inspired by tour's 6-arm design (Customisable Rubik's cube core, thing 1676041 by tour).

Several customization options are available through parameters (customizer), such as:
* The number of arms and orientation (Number_of_Arms):
All corner turning platonic and archimedean solids layouts will be available.
Currently 1,2,3,4,5,6,7abc, 8ab,12,14,20ab and 30 arm shapes implemented.
* Stem length (Length_of_Arm)
* Stem thickness (Diameter_of_arms),
* Core ball diameter (Diameter_Inner_Sphere),
* Curvature of stem endings (only curvature trough core atm, could be expanded to other on-axis centre)
* (optional): add counterscrews & Screw hole diameters
* Hollow centre (Diameter_Hollowed_Inner_Shpere)
* Symmetrical Half core (Make_two_halve_spheres), rotated to XY plane for printing.

TODO list:
* Important, urgent, easy: Fix bugs. Please comment if you find any (more).

* Important, not urgent, easy: Add option for surface turning connections