Silent pause menu option

[Edward Hart-Davis]

I think that there should be an option that would make the game silence itself when paused, so that the user could focus on other things when they need to without closing down the game.

[Riot]

add option to mute the sound when paused, resolves #289

→ <<cset 47212ce8f65a>>

[Riot]

Removing milestone: Beta (automated comment)