Add wrapped qt package as dependency fix #182

[gdolle]

see title.

[cbrnr]

Thanks @gdolle! Note that this workaround doesn't change requirements.txt, so if you do pip install -r requirements.txt you will get neither PySide2 nor PyQt5. It would be nice to keep all dependencies in requirements.txt, but I don't think this is possible. It's just one more thing to keep in mind, namely that python setup.py install is required for a working installation.

I've added an automatic flake8 check on GitHub, can you please rebase and push to see if that works?

[gdolle]

Yes it is just a workaround (but better than nothing!)

can you please rebase

Ok!

[cbrnr]

And please also add a short entry in CHANGELOG.md stating that PySide2 will be automatically installed by setuptools if neither PyQt5 nor PySide2 is installed.

[cbrnr]

Thanks @gdolle!