Add duration to posts, add posts#index for users

![image](https://cloud.githubusercontent.com/assets/8669803/5018533/8b33ceec-6a85-11e4-9272-93d916f31f39.png)

The formatting is hard to read. Here's the layout I'd prefer:

```
<td>
  <p>text</p>
  <p>text</p>
</td>
```