refine geosphere based on octahedron instead of icosahedron

[cgcostume]

Creating a geosphere based on octahedron allows for more usable uv generation (e.g. for equirectangular maps). Implementation is discussed and illustrated here: https://www.binpress.com/creating-octahedron-sphere-unity/

• create octahedron.ts
• refine icosahedron and octahedron w.r.t. latest webgl-operate naming conventions

[cgcostume]

advanced (nice to have):

• index-based triangle-strip implementation please: refer to Lindstrom and Valerio, Terrain Simplification Simplified: A General Framework for View-Dependent Out-of-Core Visualization https://www.computer.org/csdl/journal/tg/2002/03/v0239/13rRUxBrGgM