Fixed a couple of unrelated, intermittent crashes, and a menu displacement issue.

• Added “Beat the Clock” mode.
• Music stops playing when game is not the front window, or if it is minimized to the dock.
• Regular game always gets the slow music, Beat the Clock the fast music, rather than alternating the tracks.
• Fixed the “tearing” when pages move.
• Icon lightened so that it looks more like paper, less like a waffle. 🙂