Catalog: prevent adding twice the same remote
I managed to add twice the same remote URL, I think (and thought we were already actually) we should prevent that.
(1:518)$ ideascube catalog remotes list
IDEASCUBE_ID=idb_jor_alhashmi
Importing settings from ideascube.conf.idb_jor_alhashmi
[Kiwix] Kiwix ZIM content : http://catalog.ideascube.org/kiwix.yml
[OSMybon] Experimental OSM Maps catalog : http://catalog.yohanboniface.me/catalog.yml
[maps] Maps : http://catalog.yohanboniface.me/catalog.yml