Cleanup|Audio|Client: Cleaned up s_sfx.cpp/h a little
Audio|Client: Environmental audio characteristics use sector cluster granularity

Previously these characteristics used a coarser, per-sector level of
granularity. This meant that sectors comprised of multiple disjoint
geometry groups had their audio characteristics determined according
to a spacial volume derived from the united bounding rectangle of all
these groups.

Consequently reverb effects would vary significantly depending on how
the map was geometrically constructed.