Add python-imaging dependency its been a ppa dep since 2011

Add zlib1g-dev Readme.ubuntu since has been part of ppa deps for a while too
and its part of readme.linux.

Full A-Z Alphabetical sort on both readmes's as per wsnipex comments

Squash all into 1
Merge pull request #2654 from uNiversaI/patch-1

Add missing dependencies to Readme.linux and Readme.ubuntu sort alphabetically