Major default formspec style update

- Uses formspec_prepend to set e.g. button style
- Make all formspecs use the MCL2 style consistently

mods/ITEMS/mcl_furnaces/init.lua

@@ -8,7 +8,6 @@ local S = minetest.get_translator("mcl_furnaces")
 local function active_formspec(fuel_percent, item_percent)
 	return "size[9,8.75]"..
 	"background[-0.19,-0.25;9.41,9.49;crafting_inventory_furnace.png]"..
-	mcl_vars.inventory_header..
 	"label[0,4;"..minetest.formspec_escape(minetest.colorize("#313131", S("Inventory"))).."]"..
 	"list[current_player;main;0,4.5;9,3;9]"..
 	"list[current_player;main;0,7.74;9,1;]"..
@@ -32,7 +31,6 @@ end
 
 local inactive_formspec = "size[9,8.75]"..
 	"background[-0.19,-0.25;9.41,9.49;crafting_inventory_furnace.png]"..
-	mcl_vars.inventory_header..
 	"label[0,4;"..minetest.formspec_escape(minetest.colorize("#313131", S("Inventory"))).."]"..
 	"list[current_player;main;0,4.5;9,3;9]"..
 	"list[current_player;main;0,7.74;9,1;]"..