Added privy doors back in, a few backend cleanups to remove non-critical errors.

Retrofitted code that was broken by vanilla hotfix of March 6, 2019. Doors should all open & close again.

Fixed crafting bug for new small door -- it's now properly a variant under the regular door

Added new flat-top variant with thin vertical planks set in horizontal-slat frame.

Updated the SBC for the Bulkhead doors with a lot of commenting to help explain the new animation and model-attachment system. Also added more detail to iron gate.

Moved over all animation to new 0.6.4 settings

Added cellar bulkhead door