graphics/py-pillow: Update to 5.0.0

• Update to 5.0.0
• Add TEST_DEPENDS, which was missing in previous port versions where test target was defined.
• Switch to using pytest, per upstream.
• Add comment to track actual (precise) supported Python versions.

Release Notes:

• https://pillow.readthedocs.io/en/latest/releasenotes/index.html

Backward Incompatible Changes (5.0.0):

• https://pillow.readthedocs.io/en/latest/releasenotes/5.0.0.html#backwards-incompatible-changes

Detailed Changelog:

• https://github.com/python-pillow/Pillow/blob/5.0.0/CHANGES.rst

PR: 226573 [1]
Submitted by: Kevin Golding <ports caomhin org> [1]