Dynamic storypackage

It's become apparent that due to their dynamic nature, there is not a one-size-fits-all container to use in story package. Therefore, this introduces some logic to pick an appropriate `ContainerDefinition` layout depending on the size of the story package.

We use a custom container for, 1, 2, 3 & 5 items and all other numbers use the normal `fixedMediumFastXII` which caters well for even numbers.

### One item
![google chrome](https://cloud.githubusercontent.com/assets/80089/4806502/1b2b6e68-5e8a-11e4-94c7-75da0be71075.png)

### Two items
![google chrome](https://cloud.githubusercontent.com/assets/80089/4806513/2c7db8a6-5e8a-11e4-82df-2283baca583a.png)

### Three items
![google chrome](https://cloud.githubusercontent.com/assets/80089/4806517/32ebc2be-5e8a-11e4-8474-a6711be79f1a.png)

### Five items
![google chrome](https://cloud.githubusercontent.com/assets/80089/4806523/3a63971a-5e8a-11e4-9ef1-b5606c6cdf41.png)

/cc @Pearson82 @sammorrisdesign @robertberry 
Remove `more-on-this-story--one-item` from _related.scss?