Added hitsounds

Cvars added:

g_hitsounds
  0 - off
  1 - humans only
  2 - humans and aliens

g_hitsoundsType
  0 - hit count
  1 - hit damage

g_hitsoundsFriendly
  enable hitsounds for friendlies

g_hitsoundsBuildable
  enable hitsounds for buildables

Co-Authored-by: Jeff Kent <jeff@jkent.net>