User can add images to feed updates

I'm not actually bored.

https://trello.com/c/l9NNSZud/50-status-update-image

![image](https://cloud.githubusercontent.com/assets/8669803/5127591/2c67b03a-70a3-11e4-838f-fad45d046f1f.png)
no need for `<p>` tag wrapper I'd think