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
Update product page links & 4.4 docs link messages
Fixing feature link in sidebar menu
Using right redirects for 5 downloads
Merge pull request #665 from hflynn/rebased/develop/release_updates

Update 5 docs for release changes  (rebased onto develop)
Merge remote-tracking branch 'origin/develop'

Conflicts:
	omero/themes/globalomerotoc.html
Merge pull request #671 from hflynn/rebased/develop/downloads_5

Using right redirects for 5 downloads (rebased onto develop)
Merge pull request #660 from sbesson/rebased/develop/pillow

Update documentation to use Pillow instead of PIL (rebased onto develop)
Clarify 64 bit python docs
Remove PyWin32 readme link

It goes via an adverts page, and is auto displayed on the downloads page anyway.
Add note about 64-bit ice paths
Hypenate 32/64-bit
Make it clearer that versions apply to precompiled pkgs.
Other minor fixes.