[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/org/bukkit/craftbukkit/block/CraftBrewingStand.java

@@ -4,8 +4,8 @@ import net.minecraft.server.TileEntityBrewingStand;
 import org.bukkit.block.Block;
 import org.bukkit.block.BrewingStand;
 import org.bukkit.craftbukkit.CraftWorld;
-import org.bukkit.craftbukkit.inventory.CraftInventory;
-import org.bukkit.inventory.Inventory;
+import org.bukkit.craftbukkit.inventory.CraftInventoryBrewer;
+import org.bukkit.inventory.BrewerInventory;
 
 public class CraftBrewingStand extends CraftBlockState implements BrewingStand {
     private final CraftWorld world;
@@ -18,8 +18,8 @@ public class CraftBrewingStand extends CraftBlockState implements BrewingStand {
         brewingStand = (TileEntityBrewingStand) world.getTileEntityAt(getX(), getY(), getZ());
     }
 
-    public Inventory getInventory() {
-        return new CraftInventory(brewingStand);
+    public BrewerInventory getInventory() {
+        return new CraftInventoryBrewer(brewingStand);
     }
 
     @Override