Pause music when volume is 0

Music was played in background even when volume was 0, this resulted in
30kb / s constant diskreads which can cause stutter if a platter-disk is already
under heavy load (torrents etc)
Optimized build range ring on selection of ENGINEER units
Optimized filtering of factories in rallypoint beat function
Selection Range Overlay now only works for single units

See issue #94
Reduced wreck debris projectiles

Reduced the amount of wreck debris projectiles with ~50%.

Every time a unit dies it spawns alot of projetiles which are randomly shot
away from the wreck. This takes unnecessasry toll on the simulation,
especially when there are units dying constantly all over the field.

Most of the time people won't even see these but they still take up as
much CPU-resources.
Bugfix with /windowed
Minimum TargetCheckInterval set to 0.3 to reduce load