[Bleeding] Implementation of inventory framework. Addresses BUKKIT-856

See the corresponding Bukkit commit for details.

Implementation details:
- Any packets that include an itemstack will send air stacks as null; maybe this will even eliminate the client crash that occurs if the client receives an air stack
- Better handling of null itemstacks in general (ie less converting them to air stacks)
- Inventory.setContents() can now take an array smaller than the inventory without error
- Player.updateInventory() should now correctly update the result slot in a crafting inventory

Some small credit goes to Afforess (initial implementation of openInventory() methods) and Drakia (initial implementation of InventoryOpenEvent and InventoryCloseEvent).

src/main/java/net/minecraft/server/ContainerEnchantTableInventory.java

@@ -1,8 +1,8 @@
 package net.minecraft.server;
 
-class ContainerEnchantTableInventory extends ContainerEnchantTableSubcontainer {
+public class ContainerEnchantTableInventory extends ContainerEnchantTableSubcontainer { // CraftBukkit -> public
 
-    final ContainerEnchantTable a;
+    public final ContainerEnchantTable a; // CraftBukkit -> public
 
     ContainerEnchantTableInventory(ContainerEnchantTable containerenchanttable, String s, int i) {
         super(s, i);