Slime Mob Refactor

Death of the istype invasion from slimes, previously every single color of slime was its own kind of mob, and every single one of those slimes also had an adult form which was a different mob.

There is now only one kind of slime, reliant on new var is_adult and old var colour to determine how it looks. All baby slimes functioned identically outside of icon and core, and all adult slimes functioned identically to each other and to the babys save for a bit higher Health and more capacity to break shit.

A nice side effect is that this solves any inheritence issues of baby slimes growing up since it's still the same mob, though it doesn't solve the same issues for adult slimes splitting.

Also fixed a few annoying but rare bugs (like getting ghosted because you got DC'd and your slime self split and you weren't around to get mind transfered)
Merge branch 'master' of https://github.com/tgstation/-tg-station into slimetime

Conflicts:
	code/modules/mob/living/simple_animal/simple_animal.dm
Jenkins you're a loose cannon, but you're a damn good cop.
Adds a placeholder core in case admins var edit a slime to "rainbow", which is a valid icon. They will be able to grow and breed just like a normal slime, their cores don't do anything.

fixes a bug in my own code with something that was double string'd.
Removed a bit of code from a merge conflict I apparenty resolved incompletely.

Doing great with commit numbers, as usual.
spans metroid.dm
Merge pull request #2354 from Incoming5643/slimetime

Slime Mob Refactor