horizontal rule on articles with no main media

![image](https://cloud.githubusercontent.com/assets/960919/5110123/f17e6fa8-700d-11e4-8ae6-28cf8092a203.png)

For me this look like a common object that can be used somewhere else around the page. Is it really necessary to make it as an element of content and modification? It calls for something like `.divider' and `.divider--top` or something like that.

There are dotted lines on the left side (share icons etc) so we can reuse it then there too.