when updating a storage object, then also update its source URL
when updating a storage object, then also update its source URL

We now always make sure that any changes to the `DJANGO_URL` setting are also reflected in the `source_url` field of master copies. Otherwise, when a node was not correctly configured or moves to another URL, then the `source_url` would keep the old value. That could then lead to redirection problems on nodes that fetch metadata from us.
MiltosD/CEFELRC,MiltosD/CEF-ELRC,JuliBakagianni/META-SHARE,MiltosD/CEF-ELRC,MiltosD/CEFELRC,MiltosD/CEF-ELRC,zeehio/META-SHARE,JuliBakagianni/CEF-ELRC,JuliBakagianni/META-SHARE,zeehio/META-SHARE,JuliBakagianni/META-SHARE,zeehio/META-SHARE,JuliBakagianni/CEF-ELRC,MiltosD/CEF-ELRC,zeehio/META-SHARE,MiltosD/CEF-ELRC,MiltosD/CEFELRC,JuliBakagianni/CEF-ELRC,JuliBakagianni/CEF-ELRC,MiltosD/CEFELRC,MiltosD/CEFELRC,JuliBakagianni/META-SHARE,JuliBakagianni/CEF-ELRC,zeehio/META-SHARE,MiltosD/CEFELRC,MiltosD/CEF-ELRC,JuliBakagianni/META-SHARE,MiltosD/CEF-ELRC,zeehio/META-SHARE,MiltosD/CEFELRC,zeehio/META-SHARE,JuliBakagianni/META-SHARE,JuliBakagianni/META-SHARE,JuliBakagianni/CEF-ELRC,JuliBakagianni/CEF-ELRC