URI-decode alerts header in frontend

static/js/utils/alerts.js

@@ -160,7 +160,8 @@
       var alerts;
       for (var header of response.headers) {
         if (header[0] === 'alerts') {
-          alerts = JSON.parse(header[1]);
+          var decodedHeader = decodeURIComponent(header[1]);
+          alerts = JSON.parse(decodedHeader);
           break;
         }
       }