To load the right version of qt, we need to use the same logic that the qtconsole.
Depends on it rather than copy old files.

Replace qt.py by from qtconsole import qt

qtconsole: https://github.com/jupyter/qtconsole

Plantgl (https://github.com/openalea/plantgl) has copied and modified vpltk.
But modifications had not been back propagated inside vpltk.
Update vpltk according to https://github.com/fredboudon/plantgl/blob/master/src/openalea/plantgl/gui/qt/

@Wilgawox will do the modifications reviewed by @fredboudon

When visualea is launched, there is an error because qt api is set to 1.

Then, QString are not automatically converted to Python string. This lead to a number of bugs.

One solution is to set :
export QT_API_VERSION = 2

However, it would be nice to update the file openalea.vpltk.qt.init.py

Use markdown for README.
Update the doc of the package.

vpltk import oalab for the ipython shell.
This creates circular dependencies.

Remove all these uneeded dependencies to simplify nistallation and preserve modularity.