[henshin-dev] Provide previous versions via update site

[Riegerf@xxxxxxxxxxxxxxxxxxxxxxx]

Hi everyone,

I was just installing Henshin via the update site and noticed that we  
do not offer previous versions of Henshin.
A full ready-to-run archive of old versions should be offered, as  
users might want to use a specific version, for example to aid in  
editing legacy code.

Felix