[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.
change_attribute_type('CWCache', 'timestamp', 'TZDatetime')
change_attribute_type('CWUser', 'last_login_time', 'TZDatetime')
change_attribute_type('CWSource', 'latest_retrieval', 'TZDatetime')
drop_attribute('CWSource', 'synchronizing')
add_attribute('CWSource', 'in_synchronization')