3-tier.py and mvc.py are almost identical

_3-tier.py_ and _mvc.py_ are almost identical from a high level point of view. The only difference is that in _3-tier.py_ the _logic_ instance and the _ui_ instance may be assigned to the _data_ instance explicitly. In _mvc.py_ the _model_ instance and the _view_ instance is assiged to the _controller_ instance statically during its creation.