refactor and add the ability to inject custom code

src/config-page.html

@@ -6,13 +6,15 @@
     <link rel="stylesheet" href="styles/config-page.css">
     <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no">
     <script>
+      window.returnTo = '$$RETURN_TO$$';
       window.clayConfig = $$CONFIG$$;
       window.claySettings = $$SETTINGS$$;
+      window.customFn = function() $$CUSTOM_FN$$;
     </script>
   </head>
   <body>
     <form id="main-form"></form>
     <script src="../vendor/pebble-slate/dist/js/slate.min.js"></script>
-    <script src="../tmp/config-page.js"></script>
+    <script uglify src="../tmp/config-page.js"></script>
   </body>
 </html>