Users can edit posts

https://trello.com/c/AaW2xH0d/12-as-a-user-i-can-update-my-posts

![screenshot from 2014-11-05 11 13 24](https://cloud.githubusercontent.com/assets/8154429/4920970/b5333bd0-6506-11e4-9b19-2bb05cc5003d.png)