Fix implementation on linux, this works less well as on windows.

On gnome, double call to zoom_height will move the window 10px on the left and make it slighltly bigger than the screen. Seems to be a Qt or a Gnome bug. This is not that bad, most people will only use it once.
- Add IPython shell and move from pyqode.qt to PyQt4 (because IPython does not support pyqt5)

- Add class explorer tree view
- Add action to show/hide tree view and shell