[Patch] Theme-aware city window

[eipi]

This patch enables theme support for the city info window.

I changed the minimum size of the window so that there are at most two rows of buttons at the bottom; the attached images show the minimum size of the window with both the default theme and the standard-large theme. What do you think?

[prissi]

I think the number of button line does not matter, as there are large and small screen to support ...

The size of this dialogue was to match the standard convoi window etc., so they are all tileable. (Not sure, if this was still the case).