sips issues:
- -Z apply on the destination
- -p doesn't work anymore
- --padColor is ignored
Reimplementation using Pillow also allow us to detect the lower/left pixel to determinate background color
of the launchimages.
FancyUrlopener.urlretrieve was failing on redirect, but in an insidious way, because of a bug in the python-future module:
https://github.com/PythonCharmers/python-future/issues/425
Replace with the requests module for the time being.
