* Replace ad-hoc storage code with Storage interface and FileStorage for file storage and MysqlStorage for MySQL storage. (MysqlFunctions.java sort of provided this functionality already, but it was incomplete, and lacked a file counterpart.)
* Replace homemade version-dependent serialization code with Bukkit's built-in serialization system.
* Remove dependency on craftbukkit jar, as per change of serialization code above.
* Cleaned up pom.xml to not contain repositories we don't use.