Add support for playing ogg/vorbis sounds

This works but is not optimal; the current sound system leaves a lot to be desired.

This only works for sounds (not music). See [this](https://github.com/OpenRA/OpenRA/blob/bleed/mods/d2k/notifications.yaml#L36).

Someone familiar with OpenAL should really redo the sound system with proper interfaces for the sound loaders.

See also:  #5491