Show buildings and citizens in City View

[SWY1985]

We'd need to reverse engineer the city view code in order to get the buildings to render on the correct position.

Currently implementing an algorithm that is similar, which should be good enough until we have the original rendering figured out.
Current implementation status: https://github.com/SWY1985/CivOne/wiki/Status:-City-view-rendering

It seems likely that it will be finished soon, so I added this feature to 0.1.0-alpha.1.

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For clarity, here's an overview of things to do:

• Use the correct grid to draw buildings, so buildings don't appear off screen
• Make sure at least a couple of houses are always drawn (prevent empty cities)
• Draw city improvements closer to the rest of the buildings
• Drawing order, prevent buildings from being drawn on top of each other
• Draw all wonders/buildings

[SWY1985]

Linked to #250