Exapandable most popular trails

This removes the exipired a/b test for expandable trails on story packages, and moves the functionality down to the most popular component at the bototm of each page. This is more in line with the thinking from the UX team.

## Hypothesis
Ability to expand the begining of articles will increase in-page content consumption (measured expansion of trail articles) and thus increase dwell time.

However, this may drive down the number of page views per visit. Whilst reducing the volume of trails inside the story package may have a negative affect on click throughs to those articles.

### Buckets
- Control: normal, tabbed most popular component.
- Variant A: Stacked most popular lists with expandable trails

### Predictions
- Nick: Increase page dwell time by 10%
- Patrick: Reduce story package click throughs by 15%, increase page dwell time by 5%

## Screenshots
### Before
![Before](http://cl.ly/image/1e0S2R3k261m/Image%202013.09.03%2010%3A13%3A22.png)
### After
![After](http://cl.ly/image/0p0u0h2B3f2l/Image%202013.09.03%2010%3A14%3A12.png)