Virgo 5 outdoors stuff (#16025)

Added a few V5 atmosphere variant of snow and ice turfs.

Added some rock and skeleton props for V5.

Added a V5 sprite for the overmap.

Added a V5 skybox image.

code/game/objects/structures/props/prop.dm

@@ -52,6 +52,13 @@
 	icon_state = "ship_memorial"
 	bound_width = 64
 
+/obj/structure/prop/big_skeleton
+	name = "large skeleton"
+	desc = "Whatever it is, it doesn't look too healthy."
+	icon = 'icons/obj/props/decor96x96.dmi'
+	icon_state = "big_skeleton"
+	density = 0
+
 /**
  *
  Notes on change_state

code/game/objects/structures/props/rocks.dm

@@ -59,4 +59,24 @@
 /obj/structure/prop/rock/crystal_dust
 	name = "crystal dust"
 	icon = 'icons/obj/props/decor.dmi'
-	icon_state = "bsc_dust"
+	icon_state = "bsc_dust"
+
+/obj/structure/prop/rock/ice
+	icon_state = "ice2"
+
+/obj/structure/prop/rock/ice/spike
+	icon_state = "ice1"
+
+/obj/structure/prop/rock/ice/flat
+	icon_state = "ice3"
+
+/obj/structure/prop/rock/ice/round
+	icon_state = "ice4"
+
+/obj/structure/prop/rock/ice/small
+	name = "small rocks"
+	icon_state = "icesmall1"
+	density = FALSE
+
+/obj/structure/prop/rock/ice/small/alt
+	icon_state = "icesmall2"