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.
It would be nice to document what are the events that makes the game go to each state. And which one is currently beign used and which is not unsed right now.