Modified all Zootirer's addon ships

In addition to adding the source_info element, a few png were also
updated with teh version retrieved on 31.1.14. Possibly also changes in
the XML file are being taken into account.
Fixed small errors in Zootier's ship files
Modified file from Stickymonk's site

Also updated woodchips' image.
Fixed an error in a Stickymonk's file

file: lettuce.xml
Updated README.md file