Extend forge's recipe classes

* Treat LiquidStack as a filled container.
* Add methods to get recipe input.

        // Examples.
        LiquidStack liquidWater = new LiquidStack(Block.waterStill, LiquidContainerRegistry.BUCKET_VOLUME);
        IRecipe recipe;

        // Water + snawball -> ice
        recipe = new ShapelessForgeRecipe(Block.ice,
                liquidWater,
                Item.snowball);
        GameRegistry.addRecipe(recipe);

        // 3 cacti + empty container -> container filled with water.
        recipe = new ShapedLiquidFillingRecipe(
                liquidWater,
                "ccc",
                " b ",
                Character.valueOf('c'), Block.cactus,
                Character.valueOf('b'), new ItemEmptyContainer());
        GameRegistry.addRecipe(recipe);