Biomes: Add tundra lowland with permafrost, stones, moss and snow

Move previous tundra to highland and remove the snowblocks that are
unsuitable for a fairly dry biome, use snow slabs instead.

mods/default/nodes.lua

@@ -53,6 +53,10 @@ default:dirt_with_snow
 default:dirt_with_rainforest_litter
 default:dirt_with_coniferous_litter
 
+default:permafrost
+default:permafrost_with_stones
+default:permafrost_with_moss
+
 default:sand
 default:desert_sand
 default:silver_sand
@@ -63,7 +67,6 @@ default:clay
 
 default:snow
 default:snowblock
-
 default:ice
 default:cave_ice
 
@@ -490,6 +493,34 @@ minetest.register_node("default:dirt_with_coniferous_litter", {
 	}),
 })
 
+minetest.register_node("default:permafrost", {
+	description = "Permafrost",
+	tiles = {"default_permafrost.png"},
+	groups = {cracky = 3},
+	sounds = default.node_sound_dirt_defaults(),
+})
+
+minetest.register_node("default:permafrost_with_stones", {
+	description = "Permafrost with Stones",
+	tiles = {"default_permafrost.png^default_stones.png",
+		"default_permafrost.png"},
+	groups = {cracky = 3},
+	drop = "default:permafrost",
+	sounds = default.node_sound_gravel_defaults(),
+})
+
+minetest.register_node("default:permafrost_with_moss", {
+	description = "Permafrost with Moss",
+	tiles = {"default_moss.png", "default_permafrost.png",
+		{name = "default_permafrost.png^default_moss_side.png",
+			tileable_vertical = false}},
+	groups = {cracky = 3},
+	drop = "default:permafrost",
+	sounds = default.node_sound_dirt_defaults({
+		footstep = {name = "default_grass_footstep", gain = 0.25},
+	}),
+})
+
 minetest.register_node("default:sand", {
 	description = "Sand",
 	tiles = {"default_sand.png"},