TrailRenderer: Return std::pair from GetMinMax() function
TrailRenderer: Used Clamp() utility function
TrailRenderer: Cast to int instead of short in GetSnailColorIndex()

Decreases the binary size by 16 bytes.
TrailRenderer: Moved colour_vario calculation into GetSnailColorIndex()

This simplifies the API of the GetSnailColorIndex() function
TrailRenderer: Return unsigned index from GetSnailColorIndex()