Porsche GT3 R hybrid 2.0

Special thanks to @TicusH from the official pCars forum for providing some textures!

- fixed rearwing graphic (GT3 R hybrid -> hybrid)
- added spec and fresnel files (make sure you save your old files; please tell me what you think about it, it's my first try on spec/fresnel files so far)
- added a Porsche logo to the front (inspired by @TicusH from the official pCars Forums)

(wheels not included)

- "Porsche" and "Porsche Intelligent Performance" (were in Porscha font) replaced with the actual logos

- slightly changed the shades of grey (haha) and orange

- slightly re-arranged the different Porsche/GT3 R hybrid/hybrid logos