CanPlaceOn NBT on commandblocks and structure blocks

    The command blocks and structure blocks are hard-coded to disallow placing if the player is not in creative and/or not OPed. I suggest adding an exception for if the block has the "CanPlaceOn" NBT to allow for more creativity in adventure maps. For example, maybe a survival map gives the player a starter house that the player can place anywhere they want by placing a structure block with preset NBT and a button.

    Sidenote: giving the structure block/command block the "CanPlaceOn" NBT it does highlight that block when the player is holding the item as if the player could place it.