Sound theme picker

[veloce]

Add a new settings section to choose a sound theme (or silent).

Available sounds are listed here: https://github.com/lichess-org/lila/blob/master/modules/pref/src/main/SoundSet.scala

And the assets are here: https://github.com/lichess-org/lila/tree/master/public/sound

[Kirito-Excalibur]

Can you please assign me this?

[veloce]

done!

[aherzinger]

Could you assign me?
I suppose this issue is still open.

[veloce]

No need to be assigned to start working on it. You can open a draft PR to inform people you took that issue (and we can see the progress).
Thanks!

[brandonpl8]

Should the sound theme setting belong to the boardPreferences or generalPreferences? An argument can be made for both depending on how the sound is used in the rest of the app.

[veloce]

Closed by #152