Changeset 7854 for code/trunk/src/orxonox/sound/WorldAmbientSound.cc

detached AmbientSound from BaseObject - AmbientSound can not be placed directly in a level file anymore
instead added WorldAmbientSound, a BaseObject which can be placed in a level file to create and control ambient sound

with this change, the level can be destroyed completely because WorldAmbientSound can be deleted immediately at the end of the level, while the AmbientSound remains active until it faded out.