Implement Multi-Texturing

[bcthund]

Old game engine used 8 textures that were mapped automatically according to terrain height and slope. They should be implemented again.

[bcthund]

• [x] Generic multi-Texturing
  • [x] Load multiple textures to shader
  • [x] Map textures to height ranges
  • [x] Fade between heights
  • [x] Implement textures for steep terrain

[bcthund]

• [x] Advanced multi-texturung
  • [x] Add moisture layer using noise
  • [x] Add 3D textures for moisture levels