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/items/stacks/tiles/tile_types.dm

@@ -13,12 +13,12 @@
 	w_class = 3
 	max_amount = 60
 	icon = 'icons/obj/stacks/tiles.dmi'
+	randpixel = 7
 	drop_sound = 'sound/items/drop/axe.ogg'
 
 /obj/item/stack/tile/New()
 	..()
-	pixel_x = rand(-7, 7)
-	pixel_y = rand(-7, 7)
+	randpixel_xy()
 
 /*
  * Grass