Add the shield and food icon portions of the city screen

[TomWerner]

This gets us closer to the civ3 screen and will make implementing the granary logic more visually obvious.

I had to shrink the no food and empty food icons to make them a uniform size.

Some screenshots:

Civ3 city vs the same city from a civ3 game loaded into C7 (there are still some corruption pieces we haven't hooked up, hence the difference in shields. Also factories and such).

From a new game: