Added a city

Not much different this time. Just a new city icon, plus removing the other two whimsical animals. The city is actually a unit with move 0, so notice it still has a unit "shadow" and movement box. Ideally I'd get rid of both of those.

I think I'll need some kind of modal as well.

I'm going to need to credit art authors too, so that fits well with more modals.

Art so far: my daughter made the soldier icon. City icon is CC license, from https://game-icons.net/1x1/delapouite/modern-city.html