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.
A think this documentation should go in the enum, as Qt do in all it's documentation. Here you put a link to it. As an user i would be more interested in what triggers each state. Specially coming from active to inactive or suspended and back. I understand that will it vary according to each platform so it may be hard to document it. add a "see http://doc.qt.io/qt-5/qt.html#ApplicationState-enum".