abstract most inventory handling code into a homedecor registration function

drawtype and param related defaults are being handled as well
for now we still leave the locked-node generation to locked.lua, due to its furnace-like node support

example:
homedecor.register("penbox", {
	<common defs>
	infotext=S("Penbox"),
	inventory = {
		size=8,
		formspec=…
		lockable=true -- will be supported later
	},
})

homedecor/registration_handler.lua

@@ -0,0 +1,78 @@
+homedecor = homedecor or {}
+local S = homedecor.gettext
+
+local default_can_dig = function(pos,player)
+	local meta = minetest.get_meta(pos)
+	return meta:get_inventory():is_empty("main")
+end
+
+local default_inventory_size = 32
+local default_inventory_formspec = "size[8,9]"..
+	default.gui_bg..
+	default.gui_bg_img..
+	default.gui_slots..
+	"list[current_name;main;0,0.3;8,4;]"..
+	"list[current_player;main;0,4.85;8,1;]"..
+	"list[current_player;main;0,6.08;8,3;8]"..
+	default.get_hotbar_bg(0,4.85)
+
+--wrapper around minetest.register_node that sets sane defaults and interprets some specialized settings
+function homedecor.register(name, def)
+	def.paramtype = def.paramtype or "light"
+	def.paramtype2 = def.paramtype2 or "facedir"
+
+	def.drawtype = def.drawtype
+			or (def.mesh and "mesh")
+			or (def.node_box and "nodebox")
+
+	local infotext = def.infotext
+	def.infotext = nil -- no need to register this into the global node table
+
+	-- handle inventory setting
+	-- inventory = {
+	--	size = 16
+	--	formspec = …
+	-- }
+	local inventory = def.inventory
+	def.inventory = nil
+
+	if inventory then
+		assert((inventory.formspec == nil) == (inventory.size == nil),
+			"inventory.formspec and inventory.size either have both to be set or both be left nil" )
+
+		def.on_construct = def.on_construct or function(pos)
+			local meta = minetest.get_meta(pos)
+			if infotext then
+				meta:set_string("infotext", infotext)
+			end
+
+			meta:set_string("formspec", inventory.formspec or default_inventory_formspec)
+			meta:get_inventory():set_size("main", inventory.size or default_inventory_size)
+		end
+
+		def.can_dig = def.can_dig or default_can_dig
+		def.on_metadata_inventory_move = def.on_metadata_inventory_move or function(pos, from_list, from_index, to_list, to_index, count, player)
+			minetest.log("action", S("%s moves stuff in %s at %s"):format(
+				player:get_player_name(), name, minetest.pos_to_string(pos)
+			))
+		end
+		def.on_metadata_inventory_put = def.on_metadata_inventory_put or function(pos, listname, index, stack, player)
+			minetest.log("action", S("%s moves stuff to %s at %s"):format(
+				player:get_player_name(), name, minetest.pos_to_string(pos)
+			))
+		end
+		def.on_metadata_inventory_take = def.on_metadata_inventory_take or function(pos, listname, index, stack, player)
+			minetest.log("action", S("%s takes stuff from %s at %s"):format(
+				player:get_player_name(), name, minetest.pos_to_string(pos)
+			))
+		end
+	elseif infotext and not def.on_construct then
+		def.on_construct = function(pos)
+			local meta = minetest.get_meta(pos)
+			meta:set_string("infotext", infotext)
+		end
+	end
+
+	-- register the actual minetest node
+	minetest.register_node("homedecor:" .. name, def)
+end