Fixed some crashes and added an area for villager armor

Added workaround to the crash when an item a villager is holding takes damage but is not in the village inventory.

Fixed a crash when inventory was left open when the player disconnected and upon reconnection the player entity was null for some reason (possibly hasn't been set by the time the onUpdate function is called?).

Added an area in the inventory where armor can be placed, rather than have villagers pick which armor in their inventory to wear. This required adding a new SlotArmor class since the original class is not public.
![screenshot-armorslot](https://f.cloud.github.com/assets/669925/1893334/a7966126-7a85-11e3-946e-7d0128ed08ac.png)