Add "mute" checkbox to options

A quick and easily implemented suggestion. A new “mute” checkbox in the sound options in addition to volume sliders. So when you want to temporarily mute sound (say, for a stream to turn on your favourite music) you don’t need to move the slider, then move it back when you’re finished. All you need to do is tick the checkbox. And after the checkbox is un-ticked, it’s going back to the volume it was previously set to.