Volume Control

One of the issues with this and other of my astronomy tutorials is that the sound effects could be a bit loud and jarring.  I've moved away from the keyclick sound for button presses to a softer "bomp" sound.  I've also added volume controls and a mute button so that one can control the volume of the sound effects directly within the app rather than having to use the global volume control for the device.  No changes to the core functionality of the interactive tool was made.