Changed Bukkit to Spigot

This pull request changes the server software from Bukkit to [Spigot](http://ci.md-5.net/job/Spigot/1456/).

***Why should this pull request be merged?***
Spigot is a fork of Bukkit but with many memory and cpu improvements to ensure we are prepared for an active server.
For more info, visit the [Spigot Wiki](http://spigotmc.org/wiki/about-spigot)

***Proof of testing***
Checksum of craftbukkit.jar

```
140199c346091a52045322fe0203f94b
```