Replace CProxyObject usages with ICompoundObject interface

proj/terrax/vs2013/terrax.vcxproj

proj/terrax/vs2013/terrax.vcxproj.filters

source/terrax/CommandBuildModel.cpp

source/terrax/CommandBuildModel.h

source/terrax/CommandDelete.h

source/terrax/CommandDuplicate.cpp

source/terrax/CommandModifyModel.cpp

source/terrax/CommandModifyModel.h

source/terrax/CommandPaste.cpp

source/terrax/ICompoundObject.h

source/terrax/ProxyObject.cpp

source/terrax/ProxyObject.h

source/terrax/SceneTreeWindow.cpp

source/terrax/SceneTreeWindow.h

source/terrax/mainWindow.cpp

source/terrax/terrax.cpp

source/terrax/terrax.h

source/xUI/UITree.cpp