Refactor

Modifications:
Created two big packages: "game" & "artificialintelligence". All
previously existing packages have been packaged under "game"
The old package "game" has been renamed to "world"
The class "GameEngine" has been renamed to "World"
The package "hexas" has been renamed to "mainboard"
The package "mainboard" has a sub-package "objectives"
Created new package "gameengine" containing a new class "GameEngine"

This is to provide better encapsulation, and limit cyclic package
dependencies.