Remake drawbridge editor model

[vrad-exe]

These are all variants of drawbridges as seen in-game. They are mounted directly on the surface with no embed, come in white and black versions, and can start in either position.

However, the editor model represents all of these as simple 1.5-block long angled panels, which always appear with black tiles in the lowered position:

The new model should match the in-game appearance, and have all variants (fixing #1139 would make this possible).