Better usage of the UUIDFetcher

Now uses the ability to fetch multiple uuids at once, I also created
getters and setters instead of using public static variables. (I had
some spare time ^^). Besides this the JavaPlugin#getDataFolder() method
is now used, instead of typing it manually.
Merge pull request #5 from Buxdehuda/master

Better usage of the UUIDFetcher