Upgrade package requirements to match upstream Girder
Upgrade package requirements to match upstream Girder

Celery changes at:
http://docs.celeryproject.org/en/latest/changelog.html#version-3-1-23

Pillow changes at:
https://github.com/python-pillow/Pillow/blob/master/CHANGES.rst#320-2016-04-01

PyMongo changes at:
http://api.mongodb.com/python/current/changelog.html#changes-in-version-3-2-2

pytz changes not available.

Requests changes at:
http://docs.python-requests.org/en/master/community/updates/pytz

girder/girder_worker,girder/girder_worker,girder/girder_worker