[WIP]Chance several zombies color to better differentiate them.

As mentioned in issue #5196. I recolored some zombie to better differentiate them.
Zombie soldier: Was green; now green with light blue background. To differentiate it from fat zombie - which is much weaker, slower and in general much less dangerous.

Zombie master: Was pink; now pink with cyan background. Master is a dangerous and rare variant so I think he deserve a background. Cyan background should be distinct enough IMO.

Zombie scientist: Was white; now white with light cyan background, no longer share the same white glyph with Skeleton. The light background is a subtle hint at the (zombie) shocker - because butchering scientist can yield CBM too.

Zombie smoker: Was light gray; now light gray with white background. The white back ground is to represent smoke (which is gray 8 and white 8) and to be different from fungal which is pure light gray.

Talking about background, I'm not sure what's the official stance about this. Is background reserved for special zombies only? Also, how much "special" to qualify a background? Can background be used for weak/average zombies but have special properties (spitter come to my mind as it is not really a rare and "bossy" type of zombie but has a background nonetheless). What about crawler? decaying zombie?
Tell me what you guys think about this recolour. I try to not nullifying Candlebury's PR too much here. I may do a de-background for crawling zombie.