Move component_manager to a separated object. - component_manager is a mixin for domview. - domview inherit component_manager to mixing-in component_manager. - There is no boundary between component_manager and domview, hard to be managed and reused. - component_manager is a separated object that hold a reference to corresponding domview. - domview delegate attribute accessing to component_manager object to expose attributes and methods of component_manager. (__getattr__()) - component_manager is still a mix-in of domview.