Cut to bare bones implementation that works using the new Encounterable superclass.
Fixed to work with new Encounter design.
Modified to work with planet difficulty and Encounterable objects.
Created Encounterable superclass for encounter system.
Now extends Encounterable.
Now extends Encounterable.
Now has a difficulty enum.
Now extends Encounterable.
Assigns difficulty to planets (always EASY)
Now extends Encounterable.