Show the image button only if editing admin pages

That's the only place where we need to attach images so far.

app/assets/javascripts/ckeditor/config.js

@@ -94,8 +94,12 @@ CKEDITOR.editorConfig = function( config )
     { name: 'paragraph', groups: [ 'list' ], items: [ 'NumberedList', 'BulletedList' ] },
     { name: 'links', items: [ 'Link', 'Unlink' ] },
     { name: 'styles', items: [ 'Format' ] },
-    { name: 'insert', items: [ 'Image' ] },
     { name: 'basicstyles', groups: [ 'basicstyles', 'cleanup' ], items: [ 'Bold', 'Italic', 'Underline', 'Strike' ] }
   ];
+
+  config.toolbar_admin = config.toolbar_mini.concat([
+    { name: 'insert', items: [ 'Image' ] }
+  ]);
+
   config.toolbar = "mini";
 };