Merge pull request #659 from ximenesuk/import-fixes-dev

Update docs for import and logging fixes (rebased on develop)
Replace all occurences of PIL/Python Imaging Library by Pillow

As of 5.0.0, we start using Pillow as the default imaging library for Python.
This commit makes the corresponding changes under the existing documentation
pages.
Add section to server upgrade page about Pillow/PIL
Fix Pillow downloads page URL
Replace list of packages by see also link to server installation
merge develop -D org -I include -E exclude: PR 626 (Add new Squash tutorial and screenshots)
merge develop -D org -I include -E exclude: PR 660 (Update documentation to use Pillow instead of PIL (rebased onto develop))