Added Bacon2D::State enum and gameState property to Game. 

Added Bacon2D::State enum and gameState property to Game.  Pausing the game should be done by setting Game.gameState to Bacon2D.Paused.  This also listens to Qt.ApplicationState changes and sets Game.gameState to Bacon2D.Suspended if Qt.ApplicationState isn't active and the game isn't paused.  Setting gameState to Paused or Suspended also sets currentScene.running to false.
Thanks,I expanded the docs for Game::gameState.  The enum is more generic, but the property it is used for should be well documented.  Let me know what you think of the docs for Game::gameState.