Implement functions from Sümbül 2016 paper

[JLrumberger]

Lisa wants these two methods implemented

input: h x w x z x 1 with segments

2.2 is already implemented in https://github.com/Kainmueller-Lab/brainbow/blob/main/supervoxelize.py#L53C1-L54C1
image: RGB image
sv_label: watershed supervoxels with labels
sv_image: supervoxels filled with mean color from RGB image

(2.3) split supervoxel with different colors
--> not implemented yet

(2.4) demix/merge supervoxel
--> not implemented yet