New tool: Large Steel Pickaxe

The steel pickaxe is an uncraftable pickaxe, that can only be found inside the Mineshafts. The pickaxe itself is a longer lasting iron pickaxe, that deals more damage, and is slower to swing around. This item would create a better swapout for iron pickaxes, in case it the player is using them to make their diamond pickaxe last longer (using iron so the diamond won't be used up too fast).