Adds Skrell Shared Dreaming (#5707)

Implements skrell shared dreaming.

Whilst Unconscious and alive, skrell will enter the Srom, aka Dream, in which they telepathically link to one another.
In game, they will appear in a custom area, able to communicate with one another.
Whilst in Srom, skrell find it very hard to keep their own secrets, if not impossible, and will often 'mumble' important information.

code/game/objects/effects/landmarks.dm

@@ -79,6 +79,10 @@
 			asteroid_spawn += loc
 			delete_me = 1
 			return
+		if("skrell_entry")
+			dream_entries += loc
+			delete_me = 1
+			return
 
 	landmarks_list += src
 	return 1