Basic Shades (#79469)

## About The Pull Request

Makes shades into basic mobs. As they are solely player-controller and
have no AI, this was a very simple conversion.

Things of note:
- I've made shades use the same "theme" system as constructs, to
determine their drops and coloration - as opposed to these things being
manually set by the type of soulstone they're held in.
- I've reorganized files slightly, putting both constructs and shades in
a new "cult" basic mob folder.

That's more or less it. As I said, shades are simple.
## Why It's Good For The Game

Basic-izes another mob and cleans up the code a little. Removes the last
cult-related simplemob, too.
## Changelog
🆑
refactor: Shades now use the basic mob framework. Please report any
bugs.
/🆑

code/modules/mob/transform_procs.dm

@@ -390,7 +390,7 @@
 		return TRUE
 	if(ispath(MP, /mob/living/basic/mushroom))
 		return TRUE
-	if(ispath(MP, /mob/living/simple_animal/shade))
+	if(ispath(MP, /mob/living/basic/shade))
 		return TRUE
 	if(ispath(MP, /mob/living/basic/killer_tomato))
 		return TRUE