Quantize image to 128 colors instead of 5

Quantizing an image to five colors results in an extreme amount of
averaging of colors, leading to low chroma colors and erasing colors
from the image that the eye gravitates towards.

Coupled with a change to ensure there's still a broadly accurate signal
of a given cluster's population of the image, via summing the population
of all the clusters close to the hue of the cluster, and with proof that
having this many data points doesn't lead to instability in results,
we gain access to a much larger variety of colors. This gives room to
add heuristics to avoid 'bad' colors, as well as increase the
number of colorful colors we offer.

Bug: 189931209
Test: Test tons and tons of wallpapers over a couple days.
Change-Id: Ifc2d9393039194c151920536b9217ae9636ff0d6