Reimplement the static tractor so the game doesn't think it's a villager.

Background

The game only lets you ride a horse, so the tractor was always a horse in earlier versions of the mod. That caused issues where the game would sometimes treat the tractor as the player's horse. (For example: the horse sometimes wasn't returned to its stable overnight, or the player would start a cutscene on the horse and end it on the tractor.) Whether these issues happened depended on which the game found first, since it just takes the first horse it finds.

Tractor Mod 4.1 split the tractor into a horse tractor when the player is riding it, and a horse NPC otherwise (see #94). This fixed the horse confusion, but caused new issues where the player thinks the non-riding tractor is a villager:

Fixed in develop for the upcoming release.