Trade Registration Fix

Delays initialization of registered trades (hookshot upgrade list) until server start.
This fixes my problems with the Hookshot upgrades, and doesn't appear to cause any problems.
Fixes #18.
/**
	 * Call during FMLServerStartingEvent to register recipes, trades, and add loot.
	 * Delaying this until server start ensures that any block / item ID conflicts
	 * caused by other mods being added or removed will have been resolved.
	 */
	public static void onServerStart() {
		ZSSItems.addGrassDrops();
		ZSSItems.addVanillaDungeonLoot();
		ZSSItems.registerRecipes();
		TradeHandler.registerTrades();
	}