Added Game::State enum and state property to Game.  Pausing the game
should be done by setting Game.state to Game.Paused.  This also listens
to Qt.ApplicationState changes and sets Game.state to Game.Suspended if
Qt.ApplicationState isn't active and the game isn't paused.  Setting
state to Paused or Suspended also sets currentScene.running to false.
Merge branch 'focus_state_handling' of github.com:kenvandine/Bacon2D into focus_state_handling