Various python package updates

Commits: https://github.com/pypa/virtualenv/compare/15.1.0...16.0.0
Changelog: https://virtualenv.pypa.io/en/latest/changes/#id1

Commits: https://github.com/pypa/setuptools/compare/v39.0.1...v39.1.0
Changelog:
https://github.com/pypa/setuptools/blob/v39.1.0/CHANGES.rst#v3910

Commits: https://github.com/tox-dev/tox/compare/2.9.1...3.0.0
Changelog: https://tox.readthedocs.io/en/latest/changelog.html#id4

Commits: https://github.com/pytest-dev/pytest/compare/3.2.2...3.5.1
Changelog:
https://github.com/pytest-dev/pytest/blob/3.5.1/CHANGELOG.rst#pytest-351-2018-04-23

Commits: https://github.com/pytest-dev/py/compare/1.4.34...1.5.3

Changelog: https://github.com/pypa/setuptools/blob/v39.0.1/CHANGES.rst
Commits: https://github.com/pypa/setuptools/compare/v38.4.0...v39.0.1

Changelog: https://github.com/python-pillow/Pillow/blob/5.1.0/CHANGES.rst#510-2018-04-02
Commits: https://github.com/python-pillow/Pillow/compare/5.0.0...5.1.0

Mostly small changes, but important to note is that the legacy
OleFileIO_PL module has been dropped.

Commits: https://github.com/decalage2/olefile/compare/v0.44...v0.45.1