i will deprecate the directory view's zoom interface.

it seems zoom function let the extensiable directory view's framework become more complex.
in fact we should do a 'zoom' by providing several view's extension, instead of do them in a view.
the defect of new idea is that we might not use ctrl + mouse wheel to zoom in/out for our view.
it might have to switch the view in tool bar or in directory view's menu.