[MP] Adjust fx_rain entity to be more like SP with spawnflags.
No spawnflags - behaves as is in MP. (The count variable never did anything)
LIGHT - light rain
MEDIUM - same as no spawnflags
HEAVY - heavy downpour with fog (no lightning effects can work purely server side in MP)
ACID - acid rain (no pain)
MISTY_FOG - fog