Implement form factors for PlatonicOctahedron and PlatonicTetrahedron

PlatonicOctahedron and PlatonicTetrahedron are declared in documentation, but not implemented in code.

  • Implement FormFactor classes.
  • Add scripts to Examples/ff.
  • Add hugo pages.
  • Add to GUI. Do this together with #240 (closed)
Edited by Mikhail Svechnikov