Adds an image for outdated blog articles

An image for linking in outdated articles. Suggested markup provided to authors will be:

```
<div style="display:block; background-color:#fff">
  <img src='http://emberjs.com/images/community/outdated.png' style="float:left;">
  <p style="margin-left:115px;">
    <em>Hey!</em> This article references a pre-release version of Ember.js. Now that Ember.js has reached a 1.0 API the code samples below are no longer correct and the expressed opinions <em>may</em> no longer be accurate.
  </p>
</div>
```