shows a connection box (and only this), then if the user is an admin shows the
"Hello %s, your gallery is empty...".
I've also added the ability to deactivate this message. Only an admin can
deactivate it.
git-svn-id: http://piwigo.org/svn/trunk@5240 68402e56-0260-453c-a942-63ccdbb3a9ee