Fixed modifyFoodStackSize, addTradesButcher, addHarvestCraftChestLoot, addTradesFarmer, and added addSaplingTradesFarmer

 * modifyFoodStackSize wasn't being used (it was modifying the stack size regardless)
 * Renamed addTradesFarmer to addCropTradesFarmer
 * Used the various existing ITradeHandler implementations as a guide for which trades to add for saplings/crops
 * Closes #15