Add jshint comments in modules that require ES6

This is to supress warnings about ES6 syntax usage, all modern browsers support 'class' so it's ok

assets/static/alerts.js

@@ -1,10 +1,11 @@
+// jshint esversion: 6
+
 var Alerts = (function() {
 
 
     var silences = {},
         labelCache = new LRUMap(1000);
 
-
     class AlertGroup {
         constructor(groupData) {
             $.extend(this, groupData);

assets/static/config.js

@@ -1,3 +1,5 @@
+// jshint esversion: 6
+
 var Option = (function(params) {