Add widget for showing multiple certificates

Certs widget is based on multivalued widget and adds ability to add new certificate
and delete it. Each line is cert_widget.

https://fedorahosted.org/freeipa/ticket/5108
https://fedorahosted.org/freeipa/ticket/5381

Reviewed-By: Petr Vobornik <pvoborni@redhat.com>

ipaserver/plugins/internal.py

@@ -385,6 +385,7 @@ class i18n_messages(Command):
                 "cessation_of_operation": _("Cessation of Operation"),
                 "common_name": _("Common Name"),
                 "download": _("Download"),
+                "delete_cert_end": _("the certificate with serial number "),
                 "expires_on": _("Expires On"),
                 "find_issuedon_from": _("Issued on from"),
                 "find_issuedon_to": _("Issued on to"),