Added sound_emitter; some refactor; small bugfix

proj/sxgame/vs2013/sxgame.vcxproj

proj/sxgame/vs2013/sxgame.vcxproj.filters

source/core/TaskManager.cpp

source/core/TaskManager.h

source/game/SoundEmitter.cpp

source/game/SoundEmitter.h

source/game/SoundPlayer.cpp

source/terrax/terrax.cpp

source/xEngine/Engine.cpp

source/xSound/SoundEmitter.cpp

source/xSound/SoundLayer.cpp

source/xSound/SoundLayer.h

source/xSound/SoundLoader.cpp

source/xcommon/IXSoundSystem.h