Build Banks and Markets

We can build a Wood Storage, so we should also be able to build Banks to store coins and Markets to store food. This way we can take our castle system one step further and build an actual city with some sort of an economy. It may even allow for "professions", e.g. tribes with the Saw skill can provide the wood, tribes with Hunting or Farming skills can supply the food, and tribes with Rogues or Miners can supply the coins. In the end, everyone works together to maintain the castle/city.