ECEditorWindow: Remove declaration for unimplemented RemoveCommand::RecreateContent function. Pass and store scenes in C++ code properly as shared/weak_ptrs. SceneTreeWidget: do not crate UndoManager in the ctor and hardcode it to use main camera scene as SceneTreeWidget has SetScene function. Move template<> bool EditAttributeCommand<Color>::mergeWith(const QUndoCommand *other) from .h to .cpp in order to fix OSX/GCC linker issues.