Add shortcut to turn on / off sound

[marijnkampf]

Is there a keyboard shortcut to turn the sound on and off for videos in the latest RPS? The grandkids are loving the random shows of their videos, but the grandparents would like a simple way to turn the sound on and off. 😀

By the way, I know how to do it by bringing up the settings (S key) and changing them, but that's a bit more than other family members can deal with.

Thanks.

-- Ben