Re-add popper.js to fix target label tooltips

Signed-off-by: Julius Volz <julius.volz@gmail.com>

web/ui/templates/_base.html

@@ -6,6 +6,7 @@
         <title>{{ pageTitle }}</title>
         <link rel="shortcut icon" href="{{ pathPrefix }}/static/img/favicon.ico?v={{ buildVersion }}">
         <script src="{{ pathPrefix }}/static/vendor/js/jquery-3.3.1.min.js?v={{ buildVersion }}"></script>    
+        <script src="{{ pathPrefix }}/static/vendor/js/popper.min.js?v={{ buildVersion }}"></script>
         <script src="{{ pathPrefix }}/static/vendor/bootstrap-4.1.3/js/bootstrap.min.js?v={{ buildVersion }}"></script>
 
         <link type="text/css" rel="stylesheet" href="{{ pathPrefix }}/static/vendor/bootstrap-4.1.3/css/bootstrap.min.css?v={{ buildVersion }}">