Add option to play sound when muted or unmuted (disabled by default)

[nicooprat]

Thanks for this plugin!

This PR adds sounds from https://rcptones.com/dev_tones/ (check beep_short_on and beep_short_off) when muted or unmuted.

It's disabled by default, I added a very simple option page to turn it on.

Tested on latest Chrome & Firefox. To test it as a temporary plugin in Firefox, this should be added in the manifest:

"applications": {
  "gecko": {
    "id": "YOUR_EMAIL_ADDRESS",
    "strict_min_version": "53.0"
  }
}

What do you think?

[nicooprat]

@mattsimonis Hi, did you have any chance to have a look at this PR? I'm using it as is for a few month now and didn't find any bug. I just merged your latest changes about the new Google Meet UI too.

Thanks!

[magnetikonline]

This looks great @nicooprat. What do you think @mattsimonis? Seems like a really nice addition to your very handy plugin. 👍