update to LibRaw 0.16.0, load x-trans images

- Use LibRaw 0.16.0 to load x-trans images
- LibRaw >= 1.15.0 no longer allows document_mode (which returned
  grayscale uninterpolated data), hence now receive multi-channel
  data then copy it to dt single-channel mosaic format
- Cull unneeded libraw parameters which pertain to output.
- Libraw scales colors and subtracts black point, so no need to do this
  in dt_imageio_open_raw()
- For x-trans images, on image load orient/shift the mosaic pattern
  depending on orientation & usable image area.
- No longer blacklist x-trans raw files