pythonPackages: update setuptools, many updates and fixes

[FRidh]

I intended to update only a few packages, but due to all sorts of dependencies this PR got a bit bigger than planned. The reason why this PR is so large is that setuptools had to be upgraded which had a sizeable fall out.

Important changes:

• setuptools is upgraded from 18.2 to the latest, 19.4. Since 18.4, setuptools will always try to run tests. This can cause lots of vague errors (often ImportError) during checkPhase. See Python: packages require newer setuptools because of environment markers #12565 for more. On the somewhat positive side, this helps us to detect false positives, i.e. packages that used to pass the tests but now don't because the test runner was simply not invoked correctly.
• pep8 and flake8 now support Python 3.5
• twisted is now version 15.5. The old 11.1 is available as twisted_11.
• xray has become xarray, since upstream changed their name.

Progress on Hydra

https://headcounter.org/hydra/jobset/iElectric/python-wip/evals

[mention-bot]

By analyzing the blame information on this pull request, we identified @roblabla to be a potential reviewer

[FRidh]

Updating ipython and/or pip results in the following error:

error in ipython setup command: Invalid environment marker: sys_platform == "darwin" and platform_python_implementation == "CPython"

See also ipython/ipython#9159

[FRidh]

Some pypy packages build but cannot install the wheel:

• urwid: https://headcounter.org/hydra/build/869239/nixlog/1/raw
• PyStemmer: https://headcounter.org/hydra/build/871408/nixlog/1/raw
• ldap: https://headcounter.org/hydra/build/874586/nixlog/1/raw
• lxml: https://headcounter.org/hydra/build/869337/nixlog/1/raw

Related issue: gevent/gevent#722
And at Pip: pypa/pip#3414

They all seem to be having extension types but supposedly are supported on pypy.
Any ideas @domenkozar ?

[FRidh]

At some point we wanted to upgrade to setuptools 19.6 as well, however, due to some difficulties that was not possible. See also https://bitbucket.org/pypa/setuptools/issues/490/upgrading-194-196-breaks-pyramid_mako