Adds a pause layer to helloworldlayer after home button tap.

Loads a pause layer to the hellowordlayer if the player hits the home
button (or is otherwise taken from the game).  This fix has a glitch,
though.  If a player exits the game via the home button, and then goes
back to the menu, and then launches a new game from the menu, the game
will not launch, but the music will begin.