Implement expansion capturing logic

[krogenth]

As a game progresses, we will need to expand our claim of territory in the map. While the Strategist does provide a BWAPI::UnitTypes::Zerg_Hatchery for workers to morph into, currently workers will only pick the nearest open BWEB block the hatchery fits in. We will need to add logic to both the worker and strategist to handle if we should take an expansion, and which expansion we should take. Typically, the first expansion will always be the "natural", which typically holds more minerals, a geyser, and is typically the closest base by ground distance. All expansions after the natural expansion can be arbitrarily determined by the strategist based on some form of criteria(is it possible to secure, is the enemy there or near by, can we give enough supplies(workers, defense, etc.) to an expansion, really whatever you can think of).

With this, the worker building a hatchery should request if this is meant to be an expansion, and if so, query what expansion is best.