More initialize tweaks (#2971)

changes:

Organs now use Initialize().
The observe message now shows the configured respawn delay instead of always 30 minutes.
Seed datums no longer have a timer in New().
External organs no longer have a timer in New()/Initialize()
Converted some spawns in organs to timers.
Floor init no longer breaks to plating first for mapped in tiles.
Added the INITIALIZE_IMMEDIATE macro to make Initialize() not wait for SSatoms init.
Mannequins now use INITIALIZE_IMMEDIATE instead of a custom-defined New().
Mannequins (from get_mannequin) now delete themselves if unused for 5 minutes or longer.

code/modules/organs/organ_stump.dm

@@ -3,7 +3,7 @@
 	icon_name = ""
 	dislocated = -1
 
-/obj/item/organ/external/stump/New(var/mob/living/carbon/holder, var/internal, var/obj/item/organ/external/limb)
+/obj/item/organ/external/stump/Initialize(mapload, var/internal, var/obj/item/organ/external/limb)
 	if(istype(limb))
 		limb_name = limb.limb_name
 		body_part = limb.body_part
@@ -11,7 +11,7 @@
 		joint = limb.joint
 		parent_organ = limb.parent_organ
 		wounds = limb.wounds
-	..(holder, internal)
+	. = ..(mapload, internal)
 	if(istype(limb))
 		max_damage = limb.max_damage
 		if((limb.status & ORGAN_ROBOT) && (!parent || (parent.status & ORGAN_ROBOT)))