Ports table item autoalign from Bay (#6946)

Made it so items get their pixel x/y reset on pickup.
    Thrown items now also get their pixel placement slightly randomized.
    Tweaked the center of mass on a boatload of items to be more accurate to their sprite art.
    Replaced a bunch of randomized pixel placement code into a unifying proc; randpixel_xy() that uses an item's randpixel var.

code/game/objects/structures/stool_bed_chair_nest/bed.dm

@@ -213,6 +213,7 @@
 	desc = "A collapsed roller bed that can be carried around."
 	icon = 'icons/obj/rollerbed.dmi'
 	icon_state = "folded"
+	center_of_mass = list("x" = 17,"y" = 7)
 	w_class = 4.0 // Can't be put in backpacks. Oh well.
 
 /obj/item/roller/attack_self(mob/user)

code/game/objects/structures/stool_bed_chair_nest/stools.dm

@@ -5,6 +5,8 @@
 	desc = "Apply butt."
 	icon = 'icons/obj/furniture.dmi'
 	icon_state = "stool_preview" //set for the map
+	randpixel = 0
+	center_of_mass = null
 	force = 10
 	throwforce = 10
 	w_class = 5