Release Manager migration to a new server

[Romain Bouvier]

Hi fellow dev,

I switched our (old) release manager from one of our old dying server at uNamur to a new one at Gandi.
New ruby version, some fixes, postgresql->mysql migration.
You should not see any differences, but if you encounter problems on next release, ping me :)

Hopefully we will get rid of the release manager in it current state once we migrated to gitlab, but we need to find alternatives for release workflow (mail to announce list, feeding of archive.xfce.org etc)

Enjoy,

Romain,