message: Replace Structure forward declare with include
  The StructureClass enum is needed, so a full header include is required.
diff: #include "../Common.h"
  #include "../Constants.h"
  -
  #include "../PopulationPool.h"
  #include "../Population/Population.h"
  -
  #include "../StorableResources.h"
  -
  #include "../RobotPool.h"
  +#include "../Things/Structures/Structure.h"
  #include "../UI/Gui.h"
  #include "../UI/UI.h"
  @@ -34,7 +32,6 @@ namespace micropather {
  class Tile;
  class TileMap;
  -class Structure;
  enum PointerType
  