make deconstruction its own system

src/lib/sim/Simulation.h

@@ -26,6 +26,7 @@
 class AiSystem;
 class BuildingSystem;
 class ConstructionSystem;
+class DeconstructionSystem;
 struct Command;
 class Hasher;
 class CombatSystem;
@@ -220,6 +221,7 @@ private:
     BeltSystem                        m_beltSystem;
     std::unique_ptr<BuildingSystem>   m_buildingSystem;
     std::unique_ptr<ConstructionSystem> m_constructionSystem;
+    std::unique_ptr<DeconstructionSystem> m_deconstructionSystem;
     std::unique_ptr<ShipSystem>       m_shipSystem;
     std::unique_ptr<AiSystem>         m_aiSystem;
     std::unique_ptr<MovementIntentSystem> m_movementIntentSystem;