Need to update sound code to cleanly use libopenal versions > 1.18.0

[pjbroad]

Issue https://github.com/raduprv/Eternal-Lands/issues/50 reported that sound was broken for libopenal versions > 1.18.0. This has been fixed with commit https://github.com/raduprv/Eternal-Lands/commit/dfb1c7a9e4e774bf14989e9e2879b1e018040093 but only as a work around. The sound code needs to be refreshed to handle the libopenal change as intended, see https://github.com/kcat/openal-soft/issues/126.