New download link

This updates the docs to point at the new downloads location for 4.4.9 as well as 5. Currently points to top level so you have to click on version number; we can decide if we want to point specifically at version 4 latest releases only when Andrew is back to put in a latest/ redirect.
(I've pointed out 4.4 versions specifically in some places)

(@sbesson)

This effectively rebases #539