Images resize to be consistent

https://trello.com/c/CFfdsllG/20-as-a-user-i-can-see-an-improved-and-consistent-layout-for-images-and-posts
![image](https://cloud.githubusercontent.com/assets/8681076/4954786/d06cac80-668f-11e4-8403-b2ece2b34739.png)

Style should live in `app/assets/stylesheets/application.css.

Also, I don't believe you need to specify the width. It will automatically resize height and maintain aspect ratio.