Fix appveyor build
So with the migration to python 3.5, we broke a couple of things on appveyor :
- No prebuild binary for pyqt 5.5.1 for python 3.5? It seems like we have to wait for PyQt 5.6. In the meantime, we are missing a conda package for PyQt5...
- cx_freeze cannot be installed on windows via pip ( https://bitbucket.org/anthony_tuininga/cx_freeze/issues/56/missed-cxfreeze-postinstall-script-in )