Support for Ogg Opus sound effects

[peter1138]

This change probably slipped under the radar, and hardly anyone actually includes sound effects in their NewGRFs so it's not that important.

OpenTTD 15 will support sound effects in Ogg Opus format. This lossy audio compression format will reduce the filesize of audio samples by about 10-20x depending on quality level.

Ogg Opus was chosen as a modern codec that is higher quality and doesn't suffer from the same issues (unavoidable pre-delay) as MP3 encoding.