Minor fixes

1. Improve const correctness in a few places (such as `Container::getMaxStackSize()` -> `Container::getMaxStackSize() const`)

2. Use C++11 varargs for `I18n::get`, `Entity::newDoubleList` and `Language::getElement`

Minecraft.World/BeaconMenu.h

@@ -14,7 +14,7 @@ private:
 		PaymentSlot(shared_ptr<Container> container, int slot, int x, int y);
 
 		bool mayPlace(shared_ptr<ItemInstance> item);
-		int getMaxStackSize();
+		int getMaxStackSize() const;
 	};
 
 public: