Add WithSellSounds & upgrade to rules

WithSellSounds[.SellSounds] replaces Building.SellSounds but can be applied to non-building actors.
The reason for keeping it separate from Sellable, is that sometimes Building defined SellSounds where Sellable was not present and the SellSounds was and still is used through inheritance.
Why the extra trait here and not just add it to Sellable? That avoids a trait lookup later. It can be disabled by just keeping this empty.