Adding a new article template which includes a cover photo

Adding a new article template which includes a cover photo. Just like on Medium posts.

Here is a demo
![screen shot 2014-04-15 at 22 01 18](https://cloud.githubusercontent.com/assets/433834/2713065/25f1a7f6-c4e1-11e3-9c99-a60ac4e2213d.png)
![screen shot 2014-04-15 at 22 01 01](https://cloud.githubusercontent.com/assets/433834/2713066/25f2cfc8-c4e1-11e3-8119-3e05c3439987.png)