Fix regression of guides page styles.

The main styles were restricted to panel body, but guides and others
were containers, not panels, so the styles did not get applied.

Now guides, videos, comments are all panels.

template/app/view/comments/Index.js

@@ -2,7 +2,7 @@
  * Container for recent comments listing.
  */
 Ext.define('Docs.view.comments.Index', {
-    extend: 'Ext.container.Container',
+    extend: 'Ext.panel.Panel',
     alias: 'widget.commentindex',
 
     cls: 'comment-index iScroll',

template/app/view/guides/Container.js

@@ -4,7 +4,7 @@
  * Renders the guide and print button.
  */
 Ext.define('Docs.view.guides.Container', {
-    extend: 'Ext.container.Container',
+    extend: 'Ext.panel.Panel',
     alias: 'widget.guidecontainer',
     componentCls: 'guide-container',
 

template/app/view/videos/Container.js

@@ -4,7 +4,7 @@
  * Renders the video itself and its title + description.
  */
 Ext.define('Docs.view.videos.Container', {
-    extend: 'Ext.container.Container',
+    extend: 'Ext.panel.Panel',
     alias: 'widget.videocontainer',
     componentCls: 'video-container',