Destination API
Added the WorldDestination

This depends on dumptruckman/PluginBase#10
Made the destination.Util class package-default

It's a utility class for just that package.
Now registering the WorldDestination
Added ctor and equals+hashCode to WorldDestination
Now testing WorldDestination serialization
Added a test class for WorldDestination
Added the ServerInterface to the MultiverseCoreAPI

I'm not sure if that's the best way to do it...
Added the PlayerDestination
Renamed DestinationTests to DestinationsTest

Now maven will execute those tests.
Merge pull request #4 from Multiverse/destination-api

Destination api