Njb users can add images to posts

https://trello.com/c/rdMrakWG/15-as-a-user-i-can-attach-an-image-to-a-post

![screen shot 2014-11-07 at 9 38 04 am](https://cloud.githubusercontent.com/assets/8646429/4954368/d44c5a98-668b-11e4-9d36-d39ac0488497.png)