map entity cleanup

Various fixes and cleanups for map entities.

• Move some code
• Replace magic numbers
• Precache some sounds
• func_conveyor, trigger_conveyor, func_pointparticles, misc_laser, trigger_gravity now use .active instead of .state - they should be controlled by relays instead of triggers now
• func_rotating no longer plays sound when it's deactivated
• fix sound for func_vectormamamam
• trigger_music can now be controlled with relays