#25 Save game and object properties

[Loid Thanead]

Properties set on objects as well as those stored in the callback should be saved as well. Probably the game properties should be moved from the callback to the game.

[Loid Thanead]

Ideally, game state should be stored in a separate object that knows how to save itself. This makes extension easier, and allows subclasses to override data formatting.

[Loid Thanead]

Game properties were moved from Callback to Game for feature request #3283413.