Added custom download URL

Made the download url's for server and cli configurable together with
productname. This to support other download location than the Xebialabs
location.
All three parameters (server, cli & productname) need to be set
otherwise the xebialabs locations are used.
Added default values to the params.pp.

Removed the https check (changed it to http) on the license file url. Now a http link can
also be provided.

Also changed a reference to "deployit-default.properties" to
"deployit-defaults.properties"