Mix N Match Units (WIP)

Instead of unlocking specific units by researching techs, unlock Chassis and Weapon types. The units you can build are a combination of the best chassis and best weapon available to you. The idea is to have "sidegrades" of similar levelled units in each era, and for different players to end up with different ones depending on the order they research techs, and on which strategic resources they have access to. Resources gate whether you can build some weapon/chassis, but you can always build the previous level if you lack the resource. E.g. You an still build Swordsmen after researching Gunpowder if you don't have Niter. Units get upgraded automatically to the best option within their PromotionClass when new parts become available, which does not cost gold. This is currently a work in progress. The scripting side is pretty much done, so it's playable, but it's missing a bunch of art defines and there aren't many new unit types yet.