Fungible door keys

[HomebrewHomunculus]

Any door key fits any iron door.

• New tag ITEM_IS_FUNGIBLE_KEY used for door keys.
• When tag TM_ACCEPTS_FUNGIBLE_KEY used for locked iron doors.
• Any key item with the tag can match any door with the tag (even if the location/machine does not match).
• Any fungible key is disposed of when used on a door with the tag (even if the location/machine does not match).
• Fungible keys don't show "from depth X" in their name when taken to other depths, since they're all the same.
• Fungible keys stack in the inventory
• 2 free extra keys at start