Content containers (Part 1 of 3)

This refactors most of the onward journey containers below content to use the new facia container patterns.

In this PR:
- Related content (now shows 8 rather than 4) 
- Story package (now shows max of 8 rather than 4) 
- Series container
- Popular in media
- Refactor discussion header styling to match new containers
- Fix tests

### Related content
![google chrome](https://cloud.githubusercontent.com/assets/80089/4752142/b44bbc10-5aa7-11e4-8551-5ac9971515e1.png)

### Series container
![google chrome](https://cloud.githubusercontent.com/assets/80089/4752145/b8ced1be-5aa7-11e4-8a2d-1176940d770c.png)

/cc @mattosborn @rich-nguyen @robertberry @sndrs 
I wonder if we should make "fixed/medium/fast-XI" a val on FixedContainers, and then just reference it within `all`. If we did that then should it ever be removed we'll get a compile time error for this template.

As the code is now, were this ever removed we'd get a runtime error when it tries to look it up in the map and it's not there.