Added allowIpod to IOSApplicationConfiguration

Added a new variable to IOSAppConfig called allowIpod in order to be able to play the game without stopping the background music from iPod app.
Also, modified the constructor of IOSAudio to pass the IOSApplicationConfiguration from IOSApplication.

See:
http://badlogicgames.com/forum/viewtopic.php?f=11&t=11544&p=51952
https://groups.google.com/forum/#!msg/robovm/3YycMw9jOzE/j2mP2RDJ-CEJ

Also, the ObjectAL library should be updated in order for this to work, but I'm not sure how to do it.