Rewritten implementation to make it much easier

[stefvanschie]

The previous impl. used two different fields for both offline players and normal players. Instead of doing that we can use on offline player and make the other methods return the normal player when appropriate. This makes the code much simpler and easy to read. API compatibility is still ensured since all public methods that were previously available are still here.

[Maximvdw]

Missed this PR. A similar fix has been made. The version is not yet publicly released