Update URLs to "external" so developer can share with multiple devices.

layouts/index.hbs

@@ -13,10 +13,10 @@
 
 <script>
   window.devTool = {
-    previewFrameUrl: 'http://localhost:{{ port }}/view/{{ baseView }}',
+    previewFrameUrl: '{{ previewFrameUrl }}',
   };
 </script>
-<iframe id="preview_frame" src="http://localhost:{{ port }}/view/{{ baseView }}" class="breakpoint"></iframe>
+<iframe id="preview_frame" src="{{ previewFrameUrl }}" class="breakpoint"></iframe>
 
 <script src="/scripts/dist/index.min.js"></script>
 </body>