[pkg] Depend on Pillow instead of PIL
The Pillow library is becoming the de-facto replacement for PIL.
It also is way simpler to install with pip than PIL.
Closes #4411354.
if versions_map['cubicweb'][0] == (3, 7, 4):
config['http-session-time'] *= 60
config['cleanup-session-time'] *= 60
config['cleanup-anonymous-session-time'] *= 60