Refactoring of game mechanics into new package

[chorhatarahuduketuri]

The mechanics for processing game turns has been moved into a new class (TurnProcessor) in a new package (gc.mechanics.turn).

This involves some major changes. Please test extensively.

Problems were encountered in formatting, particularly wrt whitespace. We should formalise whitespace and code formatting.

[adrianlshaw]

I've tested it and didn't identify any breaking changes. Thanks for cleaning the code.