Fixing place_cities()'s notworkingness, for the most part.

Includes tweaks to make somewhat smaller cities, however now they're
not all clumped into one in a restricted section of the overmap.

This includes some of Oddzball's overmapgen tweaks, but it doesn't go as
far.
https://github.com/Oddzball/Cataclysm-CZS/compare/5da2505...c0ec9b18a93acef633f070ee9111e7d5ba1fada3