Add MetaSoundPlayer sound abstraction

This is a simple, maybe simplistic, abstraction over libcanberra. It does specifically avoid libcanberra-gtk API as it relies underneath in the GDK backend, and X11. No extra info like application IDs or input event details are forwarded, as AFAIK don't really go anywhere.

Reproduction of sounds is also offloaded to a thread. I happen to have a soundcard that takes ages to wake up from power saving, so UI usually blocks on PA bringing it up. This removes the stall, consider it my personal itch.