fix books and swing's on_place to handle CONTENT_IGNORE and CONTENT_UNKNOWN and to always return their itemstacks

fix fence_with_signs check for content_ignore, prevent it to destroy unknown_nodes and always return the itemstack

let selection and buildable_to checks test for content_ignore; also fixes some border cases for banisters and replacing of unknown nodes

fix the japanese open door to use homedecor registration, and make it and its closed version use placeholders

add placeholders as not-buildable_to nodes, that can be set to prevent other nodes to build or expanded into expansions

this fixes #292

see https://github.com/t4im/profiler/#labeling

register the furnaces internally via homedecor.register as well, getting rid of the last dependency on deprecated lock-code

only set main list size if size field is given, to allow using the locked/lockable features with different listnames

streamline locked description/infotext setting; avoid double brackets "Node (Locked) (owned by .. )"

let the custom on_place of the expansion code call after_place_node to make sure infotexts and owners of locked nodes are being set

spawn lockable nodes for "inventory = { lockable = true }", and migrate all lockable nodes to this mechanism, but the furnaces

register a copy of the def instead of the passed def, this allows us later to spawn supporting nodes from the same original def

allow inventories to be locked (not just have a locked version of it being spawned later, but be locked by registration)

the code will also be used later to replace locked.lua that spawns a locked version from an unlocked version

introduce nodebox abstractions used by fences, like corner nodeboxes, and indirectly slab_x; update fences accordingly