Add a mute toggle on main page

[gavinhenderson]

Is your feature request related to a problem? Please describe.

When you are done with EyeCommander and pause it so that it stops outputting you will still hear the audio output

Describe the solution you'd like

There should be a button on the main page to allow you to mute the audio.

Describe alternatives you've considered

We could disable the audio feedback when you pause, but it can be handy to have audio feedback on but have no output when you are initially calibrating so we could not sync these options.