Add favicon, loaded from wrong location (#454)

frontend/template/index.html

@@ -5,6 +5,7 @@
         <title>Visual DL</title>
         <meta name="viewport" content="width=device-width, initial-scale=1">
         <meta http-equiv="X-UA-Compatible" content="IE=Edge">
+        <link rel="shortcut icon" type="image/png" href="/static/favicon.png" />
         <link href='https://fonts.googleapis.com/css?family=Roboto:300,400,500,700|Material+Icons' rel="stylesheet">
         <script type="text/javascript" src="https://dagrejs.github.io/project/dagre-d3/latest/dagre-d3.min.js"></script>
     </head>