Rework methods that access to ChallengesPlayerData object. Methods that access to this object will be private and use UUID and String where possible.
Add public methods that could use previously mentioned methods to access ChallengesPlayerData object.
Implement these methods in all places.
Add ability to enable/disable island storage in config (no-gui for now).
Disable challenge GUI opening, if user does not have island.
Implement all methods that were only placeholders.
Remove all unnecessary old methods.
Implement new methods in all classes.
User and Admin command now opens new GUI.