Add external group

Group can be normal, posix and external. Posix checkbox was removed and was replaced by radio for selecting group type. This adds possibility of adding of external group.

https://fedorahosted.org/freeipa/ticket/2895

ipalib/plugins/internal.py

@@ -405,7 +405,10 @@ class i18n_messages(Command):
             },
             "group": {
                 "details": _("Group Settings"),
-                "posix": _("POSIX group"),
+                "external": _("External"),
+                "normal": _("Normal"),
+                "posix": _("POSIX"),
+                "type": _("Group Type"),
             },
             "hbacrule": {
                 "any_host": _("Any Host"),