Revert "Add PIL to requirements.txt, because web.py plugin needs it"

This adds way moe than needed and includes a PIL that isn't on pypi
which breaks tests on travis-ci and a dev can't just install the
requirements.txt to ge the environment up.

This reverts commit 48eb8507a131876590cc0e80981cd52368e384ac.
requirements: added Pillow

removes the "No module named PIL" error