Skulls

This PR adds in Mob Skulls, Named Player Skulls, and the Skull item, as well as all of the necessary Bukkit APIs.

Most seems to be working well. Player can place skulls on the floor/walls, rotation works on the floor, and named player heads have their skins downloaded. All of this is saved and loaded properly. Easiest way to test names is with a heads plugin, such as [PlayerHeads](http://ci.md-5.net/job/PlayerHeads/).

Thanks to @Aaron1011 and @jkcclemens for their help with this.
Yeah, I normally get 60 or 70 a day now from following this and a few other somewhat busy projects, so I forget that people actually get them into a inbox they want to be able to read, Github & Twitch are the only ones to this email account so I dont normally worry about it ;)