[Bleeding] Inventory framework and events. Addresses BUKKIT-856

New events:
- InventoryOpenEvent
- InventoryClickEvent - detects any clicks on a slot or outside the window
  - In the creative inventory view, only clicks on the quickbar are detected
- InventoryCloseEvent
- BrewEvent - when a potion finishes brewing
- CraftItemEvent (a subevent of InventoryClickEvent) - fired when taking the crafted item
- PrepareItemCraftEvent - fired just before updating the result slot
Changes to existing events:
- EnchantItemEvent extends InventoryEvent and also has a new whichButton() method
- PrepareItemEnchantEvent also extends InventoryEvent
- FurnaceBurnEvent and FurnaceSmeltEvent now extend BlockEvent (as does BrewEvent)
- PlayerInventoryEvent is deprecated (though it never did anything anyway)
New subclasses of Inventory:
- BrewerInventory
- CraftingInventory
- DoubleChestInventory
- EnchantingInventory
- FurnaceInventory
New methods in Inventory:
- getViewers()
- getTitle()
- getType()
- getHolder()
- iterator() - Yes, inventories are now iterable!
  - The iterator is a ListIterator that does not support add or remove
New methods in Player:
- getOpenInventory()
- openInventory()
- openWorkbench()
- openEnchanting()
- closeInventory()
- setWindowProperty()
- getItemOnCursor()
- setItemOnCursor()
Other changes:
- createInventory() methods in Server to make inventories not linked to an object
- ContainerBlock is deprecated in favour of InventoryHolder
- New InventoryView class gives direct access to an inventory window!
- Removed the Slot class which did nothing and was used nowhere

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

By: Celtic Minstrel <celtic.minstrel.ca@some.place>

paper-api/src/main/java/org/bukkit/event/player/PlayerInventoryEvent.java

@@ -2,11 +2,16 @@ package org.bukkit.event.player;
 
 import org.bukkit.entity.Player;
 import org.bukkit.event.HandlerList;
+import org.bukkit.event.inventory.InventoryClickEvent;
+import org.bukkit.event.inventory.InventoryOpenEvent;
 import org.bukkit.inventory.Inventory;
 
 /**
- * Represents a player related inventory event
+ * Represents a player related inventory event; note that this event never actually did anything
+ * @deprecated Use {@link InventoryClickEvent} or {@link InventoryOpenEvent} instead, or one of
+ * the other inventory events in {@link org.bukkit.event.inventory}.
  */
+@Deprecated
 public class PlayerInventoryEvent extends PlayerEvent {
     private static final HandlerList handlers = new HandlerList();
     protected Inventory inventory;