[#69823020] - added mp3 format to bucket output and an is_enabled flag on the audio.file table; if an mp3 (or ogg) is broken, we can disable it by toggling this flag. e.g. see /bucket/ayat/17/105?audio=11 -- there is no "mp3: {}" hash because we discovered a broken mp3 on that ayah (do not yet know why)