Compute Blurhash using Image's Aspect Ratio

[Arthi-chaud]

The number of color on each axis is arbitrarily set to 4, whatever the source image's aspect ratio is.
For album covers (1:1), it is not a problem. However, for video thumbnails, the blurhash looks stretched, and thus not good.

• When computing an image's blurhash, the number of color per axis should depend on the image's aspect ratio
  • Examples: for a 16:9 image, we could have 4 on the X-axis, and 2 on the Y axis, 4:3 => 4 on the X-axis, 3 on the Y-axis