Reduce uniform count, use single-channel night

* Reduce texture uniform count from 128 to 20 (could reduce to about 16,
  if the backup code worked (which reduces LOD if too many textures are
  about to be used; the maximum seems to be 17 right now))
* A grayscale texture is sufficient for the night colors; use the second
  channel of that texture for the specular map (which conveniently has
  about as high a resolution as the night map)