Bugfix. Make sure group toggle state is persisted to browser storage.

updates #83

converse.js

@@ -3280,11 +3280,11 @@
                 var $el = $(ev.target);
                 this.$el.nextUntil('dt').slideToggle();
                 if ($el.hasClass("icon-opened")) {
-                    this.model.set({state: CLOSED});
+                    this.model.save({state: CLOSED});
                     $el.removeClass("icon-opened").addClass("icon-closed");
                 } else {
                     $el.removeClass("icon-closed").addClass("icon-opened");
-                    this.model.set({state: OPENED});
+                    this.model.save({state: OPENED});
                 }
             },