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.
Yeah i prefer that way too. Just commenting because i saw you handling gameState inside Game::onApplicationStateChanged() sou could be two "entities" messing with one property. But now i took a close look and saw that you manage the Pause state which was the case that i was thinking could be a problem. I think this patch is ready to go :P