Remember that the content was narrow before

Steps to reproduce bug:
----------------------
1. View page with narrow content
2. Edit page --> wide content (this is correct)
3. Cancel/Save
4. Page has now wide content, but should have narrow content

Fix
---
Only remember width of content when we are view a page, i.e. `do=show`

SPR-982

js/sidebar.js

@@ -270,7 +270,7 @@ jQuery(function () {
             setActive(stModes,$siteTools);
             setActive(utModes,$userTools);
 
-            if($body.is('.wide-content')) {
+            if($body.is('.do-show') && $body.is('.wide-content')) {
                 window.sessionStorage.setItem('wide-content', true);
                 isWideContent = true;
             }