Adds admin_jump_link and AI eye jumping

Also fixes a little mistake in ghost AI eye following.

code/modules/mob/dead/observer/observer.dm

@@ -499,8 +499,8 @@ This is the proc mobs get to turn into a ghost. Forked from ghostize due to comp
 
 	return ..()
 
-/proc/ghost_follow_link(var/atom/target, var/atom/ghost=src)
-	if(!target) return
+/proc/ghost_follow_link(var/atom/target, var/atom/ghost)
+	if((!target) || (!ghost)) return
 	if(isAI(target)) // AI core/eye follow links
 		var/mob/living/silicon/ai/A = target
 		. = "<a href='byond://?src=\ref[ghost];follow=\ref[A]'>core</a>"