Barbarian camps should only be spawned a minimum distance from cities #293
Description
This is an evolutionary step, useful for now when we don't add new barb camps after the game has started.
Right now, barb camps can spawn anywhere, even right next to a start location. This is not great, because it often results in the barbarians destroying an AI right at the start.
There should probably be a minimum distance of 10 between a barb camp and a city, but at least a minimum distance of 5.
Related to #292 , as they both involve improvements to the start location and refactoring the same area. Most likely, whoever picks up one of these should do the other next, as two people working on them separately at the same time would likely step on each others' toes.